diff --git a/CHANGELOG.md b/CHANGELOG.md
index 499b9b93464..712dea9e848 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 - `LinkBody` (`pylabrobot.resources.LinkBody`): one rigid member of a manipulator, an ordinary resource whose origin is a corner and which carries its `proximal_joint` and `distal_joint` as coordinates within it. The link is the line between the two joints and `length` is the distance, `None` on a member that ends the chain. A member turns about its proximal joint rather than its origin. (#1249)
 - `MechanicalGripper` (`pylabrobot.resources.MechanicalGripper`): a `LinkBody` that ends the chain, holding what it takes between two fingers. Its far end is a `tool_center_point` rather than a joint, it is sized to its body because `jaw_width` moves the fingers, and the jaws straddle the grip centre. (#1249)
 
+### Changed
+
+- `HamiltonDeck` and `HamiltonSTARDeck`: `num_tracks` replaces `num_rails` and `track=` replaces `rails=`; the old names are deprecated but keep working, as do decks saved with `num_rails`. A STAR deck counts two fewer tracks than it counted rails (STARlet 30, STAR 54) at the same positions, so a count passed positionally to `HamiltonSTARDeck` is now read as tracks.
+
 ### Fixed
 
 - Imported `unittest.mock` in `pylabrobot/centrifuge/centrifuge_tests.py` (pre-existing bug that prevented the test class from running).
diff --git a/docs/cookbook/star_movement_plate_to_alpaqua_core.ipynb b/docs/cookbook/star_movement_plate_to_alpaqua_core.ipynb
index acbf8396591..94acf6d3b1f 100644
--- a/docs/cookbook/star_movement_plate_to_alpaqua_core.ipynb
+++ b/docs/cookbook/star_movement_plate_to_alpaqua_core.ipynb
@@ -224,7 +224,7 @@
     "  name=\"wash_plate_0\"\n",
     ")\n",
     "\n",
-    "deck.assign_child_resource(mfx_carrier_tapped_plate_holder_example, rails=1)\n",
+    "deck.assign_child_resource(mfx_carrier_tapped_plate_holder_example, track=1)\n",
     "\n",
     "# Setup Magnet-carrying MFX Carrier\n",
     "\n",
@@ -243,7 +243,7 @@
     "# cavity_bottom of the well that is placed on top of it\n",
     "# use ztouch_probing to measure both \n",
     "\n",
-    "deck.assign_child_resource(mfx_carrier_magnet_example, rails=8)"
+    "deck.assign_child_resource(mfx_carrier_magnet_example, track=8)"
    ]
   },
   {
diff --git a/docs/resources/carrier/plate-carrier/plate_carrier.ipynb b/docs/resources/carrier/plate-carrier/plate_carrier.ipynb
index cfb5a304848..3a6475bfcaa 100644
--- a/docs/resources/carrier/plate-carrier/plate_carrier.ipynb
+++ b/docs/resources/carrier/plate-carrier/plate_carrier.ipynb
@@ -211,7 +211,7 @@
     "from pylabrobot.liquid_handling import LiquidHandler, LiquidHandlerChatterboxBackend\n",
     "from pylabrobot.resources import STARDeck\n",
     "lh = LiquidHandler(backend=LiquidHandlerChatterboxBackend(), deck=STARDeck())\n",
-    "lh.deck.assign_child_resource(my_plate_carrier, rails=1)\n",
+    "lh.deck.assign_child_resource(my_plate_carrier, track=1)\n",
     "await lh.setup()"
    ]
   },
diff --git a/docs/user_guide/00_liquid-handling/container_no_go_zones.ipynb b/docs/user_guide/00_liquid-handling/container_no_go_zones.ipynb
index 5968a95c525..0659bc60592 100644
--- a/docs/user_guide/00_liquid-handling/container_no_go_zones.ipynb
+++ b/docs/user_guide/00_liquid-handling/container_no_go_zones.ipynb
@@ -776,11 +776,11 @@
     "\n",
     "tip_car = TIP_CAR_480_A00(name=\"tip_carrier\")\n",
     "tip_car[0] = hamilton_96_tiprack_1000uL_filter(name=\"tips_1000\")\n",
-    "deck.assign_child_resource(tip_car, rails=1)\n",
+    "deck.assign_child_resource(tip_car, track=1)\n",
     "\n",
     "trough_car = Trough_CAR_5R60_A00(name=\"trough_carrier\")\n",
     "trough_car[0] = hamilton_1_trough_60mL_Vb(name=\"trough_60\")\n",
-    "deck.assign_child_resource(trough_car, rails=10)\n",
+    "deck.assign_child_resource(trough_car, track=10)\n",
     "\n",
     "trough = deck.get_resource(\"trough_60\")\n",
     "print(f\"Trough: {trough.name}\")\n",
diff --git a/docs/user_guide/00_liquid-handling/mixing.ipynb b/docs/user_guide/00_liquid-handling/mixing.ipynb
index c0bcb8d8aa8..9ae5e853fd2 100644
--- a/docs/user_guide/00_liquid-handling/mixing.ipynb
+++ b/docs/user_guide/00_liquid-handling/mixing.ipynb
@@ -47,12 +47,12 @@
     "from pylabrobot.resources import TIP_CAR_480_A00, hamilton_96_tiprack_1000uL_filter\n",
     "tip_carrier = TIP_CAR_480_A00(name=\"tiprack_1\")\n",
     "tip_carrier[0] = tr0 = hamilton_96_tiprack_1000uL_filter(name=\"tiprack_1_0\")\n",
-    "lh.deck.assign_child_resource(tip_carrier, rails=1)\n",
+    "lh.deck.assign_child_resource(tip_carrier, track=1)\n",
     "\n",
     "from pylabrobot.resources import PLT_CAR_L5AC_A00, Cor_96_wellplate_360ul_Fb\n",
     "plate_carrier = PLT_CAR_L5AC_A00(name=\"plate_carrier_1\")\n",
     "plate_carrier[0] = plate = Cor_96_wellplate_360ul_Fb(name=\"plate_1\")\n",
-    "lh.deck.assign_child_resource(plate_carrier, rails=10)"
+    "lh.deck.assign_child_resource(plate_carrier, track=10)"
    ]
   },
   {
diff --git a/docs/user_guide/00_liquid-handling/moving-channels-around.ipynb b/docs/user_guide/00_liquid-handling/moving-channels-around.ipynb
index 1874e3c7168..1a81b89f18e 100644
--- a/docs/user_guide/00_liquid-handling/moving-channels-around.ipynb
+++ b/docs/user_guide/00_liquid-handling/moving-channels-around.ipynb
@@ -46,7 +46,7 @@
         "# assign a tip rack\n",
         "tip_carrier = TIP_CAR_480_A00(name=\"tip_carrier\")\n",
         "tip_carrier[0] = tip_rack = hamilton_96_tiprack_1000uL_filter(name=\"tip_rack\")\n",
-        "lh.deck.assign_child_resource(tip_carrier, rails=0)"
+        "lh.deck.assign_child_resource(tip_carrier, track=0)"
       ]
     },
     {
diff --git a/docs/user_guide/00_liquid-handling/tutorial_tip_inventory_consolidation.ipynb b/docs/user_guide/00_liquid-handling/tutorial_tip_inventory_consolidation.ipynb
index 29e917d016b..a9f0afef9e2 100644
--- a/docs/user_guide/00_liquid-handling/tutorial_tip_inventory_consolidation.ipynb
+++ b/docs/user_guide/00_liquid-handling/tutorial_tip_inventory_consolidation.ipynb
@@ -97,7 +97,7 @@
     "tip_carrier = TIP_CAR_480_A00(name=\"tip_carrier\")\n",
     "tip_carrier[0] = tr0 = hamilton_96_tiprack_1000uL_filter(name=\"tr0\", with_tips=True)\n",
     "tip_carrier[1] = tr1 = hamilton_96_tiprack_1000uL_filter(name=\"tr1\", with_tips=False)\n",
-    "deck.assign_child_resource(tip_carrier, rails=10)"
+    "deck.assign_child_resource(tip_carrier, track=10)"
    ]
   },
   {
diff --git a/docs/user_guide/hamilton/star/hardware/replacing-iswap.md b/docs/user_guide/hamilton/star/hardware/replacing-iswap.md
index 94536a15d5e..12e7d19e5be 100644
--- a/docs/user_guide/hamilton/star/hardware/replacing-iswap.md
+++ b/docs/user_guide/hamilton/star/hardware/replacing-iswap.md
@@ -63,7 +63,7 @@ await star.setup()
 input("Confirm the deck is clear and press Enter to continue...")
 await star.pip.backend.position_components_for_free_iswap_y_range()
 await star.driver.iswap.move_y(y=300)
-x = star.deck.rails_to_location(star.deck.num_rails / 2).x
+x = star.deck.track_to_location(star.deck.num_tracks // 2 + 1).x
 await star.driver.iswap.move_x(x=x)
 ```
 
diff --git a/docs/user_guide/machine-agnostic-features/logging-and-validation/validation.ipynb b/docs/user_guide/machine-agnostic-features/logging-and-validation/validation.ipynb
index 9b117d9af65..cfae31b42af 100644
--- a/docs/user_guide/machine-agnostic-features/logging-and-validation/validation.ipynb
+++ b/docs/user_guide/machine-agnostic-features/logging-and-validation/validation.ipynb
@@ -36,7 +36,7 @@
     "from pylabrobot.resources import TIP_CAR_480_A00, hamilton_96_tiprack_1000ul\n",
     "tip_car = TIP_CAR_480_A00(name=\"tip_car\")\n",
     "tip_car[0] = tr = hamilton_96_tiprack_1000ul(name=\"ht\")\n",
-    "lh.deck.assign_child_resource(tip_car, rails=1)"
+    "lh.deck.assign_child_resource(tip_car, track=1)"
    ]
   },
   {
diff --git a/docs/user_guide/machine-agnostic-features/using-the-visualizer.ipynb b/docs/user_guide/machine-agnostic-features/using-the-visualizer.ipynb
index 09112122e57..1912d939eb2 100644
--- a/docs/user_guide/machine-agnostic-features/using-the-visualizer.ipynb
+++ b/docs/user_guide/machine-agnostic-features/using-the-visualizer.ipynb
@@ -166,7 +166,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "lh.deck.assign_child_resource(tip_car, rails=15)"
+    "lh.deck.assign_child_resource(tip_car, track=15)"
    ]
   },
   {
@@ -189,7 +189,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "lh.deck.assign_child_resource(plt_car, rails=8)"
+    "lh.deck.assign_child_resource(plt_car, track=8)"
    ]
   },
   {
diff --git a/docs/user_guide/machine-agnostic-features/using-trackers.ipynb b/docs/user_guide/machine-agnostic-features/using-trackers.ipynb
index 4736b756619..cceebd02bd1 100644
--- a/docs/user_guide/machine-agnostic-features/using-trackers.ipynb
+++ b/docs/user_guide/machine-agnostic-features/using-trackers.ipynb
@@ -218,7 +218,7 @@
       "metadata": {},
       "outputs": [],
       "source": [
-        "lh.deck.assign_child_resource(tip_carrier, rails=3)"
+        "lh.deck.assign_child_resource(tip_carrier, track=3)"
       ]
     },
     {
@@ -690,7 +690,7 @@
       "metadata": {},
       "outputs": [],
       "source": [
-        "lh.deck.assign_child_resource(plt_carrier, rails=9)"
+        "lh.deck.assign_child_resource(plt_carrier, track=9)"
       ]
     },
     {
diff --git a/pylabrobot/legacy/liquid_handling/backends/chatterbox_tests.py b/pylabrobot/legacy/liquid_handling/backends/chatterbox_tests.py
index efac36b4f8e..2472ee0da56 100644
--- a/pylabrobot/legacy/liquid_handling/backends/chatterbox_tests.py
+++ b/pylabrobot/legacy/liquid_handling/backends/chatterbox_tests.py
@@ -20,9 +20,9 @@ def setUp(self) -> None:
     self.backend = LiquidHandlerChatterboxBackend(num_channels=8)
     self.lh = LiquidHandler(self.backend, deck=self.deck)
     self.tip_rack = hamilton_96_tiprack_1000uL_filter(name="tip_rack")
-    self.deck.assign_child_resource(self.tip_rack, rails=3)
+    self.deck.assign_child_resource(self.tip_rack, track=3)
     self.plate = cor_96_wellplate_360uL_Fb(name="plate")
-    self.deck.assign_child_resource(self.plate, rails=9)
+    self.deck.assign_child_resource(self.plate, track=9)
 
   async def asyncSetUp(self) -> None:
     await super().asyncSetUp()
diff --git a/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_backend.py b/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_backend.py
index 666094e0fd5..fff0c00fc1a 100644
--- a/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_backend.py
+++ b/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_backend.py
@@ -151,7 +151,7 @@
 )
 from pylabrobot.resources.hamilton.hamilton_decks import (
   HamiltonCoreGrippers,
-  rails_for_x_coordinate,
+  track_for_x_coordinate,
 )
 from pylabrobot.resources.liquid import Liquid
 from pylabrobot.resources.rotation import Rotation
@@ -10046,8 +10046,8 @@ async def verify_and_wait_for_carriers(
       if isinstance(child, Carrier):
         # Get x coordinate relative to deck
         carrier_x = child.get_location_wrt(self.deck).x
-        carrier_start_rail = rails_for_x_coordinate(carrier_x)
-        carrier_end_rail = rails_for_x_coordinate(carrier_x - 100.0 + child.get_absolute_size_x())
+        carrier_start_rail = track_for_x_coordinate(carrier_x)
+        carrier_end_rail = track_for_x_coordinate(carrier_x - 100.0 + child.get_absolute_size_x())
 
         # Verify rails are valid
         carrier_start_rail = max(1, min(carrier_start_rail, 54))
diff --git a/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_tests.py b/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_tests.py
index d2f822bcd4d..807718b713b 100644
--- a/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_tests.py
+++ b/pylabrobot/legacy/liquid_handling/backends/hamilton/STAR_tests.py
@@ -674,7 +674,7 @@ async def asyncSetUp(self):
     self.tip_car = TIP_CAR_480_A00(name="tip carrier")
     self.tip_car[1] = self.tip_rack = hamilton_96_tiprack_300uL_filter(name="tip_rack_01")
     self.tip_car[2] = self.tip_rack2 = hamilton_96_tiprack_1000uL_filter(name="tip_rack_02")
-    self.deck.assign_child_resource(self.tip_car, rails=1)
+    self.deck.assign_child_resource(self.tip_car, track=1)
 
     self.plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     self.plt_car[0] = self.plate = cor_96_wellplate_360uL_Fb(name="plate_01")
@@ -696,7 +696,7 @@ async def asyncSetUp(self):
       nesting_z_height=10,
     )
     self.other_plate.assign_child_resource(lid)
-    self.deck.assign_child_resource(self.plt_car, rails=9)
+    self.deck.assign_child_resource(self.plt_car, track=9)
 
     class BlueBucket(Container):
       def __init__(self, name: str):
@@ -1756,7 +1756,7 @@ async def test_portrait_tip_rack_handling(self):
     tip_car[0] = tr = hamilton_96_tiprack_1000uL(name="tips_01").rotated(z=90)
     assert tr.rotation.z == 90
     assert tr.location == Coordinate(82.6, 0, 0)
-    deck.assign_child_resource(tip_car, rails=2)
+    deck.assign_child_resource(tip_car, track=2)
     await lh.setup()
 
     await lh.pick_up_tips(tr["A4:A1"])
@@ -1820,10 +1820,10 @@ async def asyncSetUp(self):
 
     self.plt_car = PLT_CAR_L5MD_A00(name="plt_car")
     self.plt_car[0] = self.plate = celltreat_96_wellplate_350uL_Ub(name="plate", with_lid=True)
-    self.deck.assign_child_resource(self.plt_car, rails=15)
+    self.deck.assign_child_resource(self.plt_car, track=15)
 
     self.plt_car2 = PLT_CAR_P3AC_A01(name="plt_car2")
-    self.deck.assign_child_resource(self.plt_car2, rails=3)
+    self.deck.assign_child_resource(self.plt_car2, track=3)
 
     self.STAR._num_channels = 8
     self.STAR._machine_conf = _DEFAULT_MACHINE_CONFIGURATION
@@ -1947,12 +1947,12 @@ async def asyncSetUp(self):
 
     tip_carrier = TIP_CAR_480_A00(name="tip_carrier")
     tip_carrier[1] = self.tip_rack = hamilton_96_tiprack_1000uL(name="tip_rack")
-    self.deck.assign_child_resource(tip_carrier, rails=1)
+    self.deck.assign_child_resource(tip_carrier, track=1)
 
     plt_carrier = PLT_CAR_L5AC_A00(name="plt_carrier")
     plt_carrier[0] = self.plate = agenbio_1_troughplate_190mL_Fl(name="plate")
     self.well = self.plate.get_well("A1")
-    self.deck.assign_child_resource(plt_carrier, rails=10)
+    self.deck.assign_child_resource(plt_carrier, track=10)
 
     self.star._num_channels = 8
     self.star._machine_conf = _DEFAULT_MACHINE_CONFIGURATION
@@ -2171,7 +2171,7 @@ async def asyncSetUp(self):
     self.lh = LiquidHandler(self.backend, deck=self.deck)
 
     self.tip_car = TIP_CAR_480_A00(name="tip_carrier")
-    self.deck.assign_child_resource(self.tip_car, rails=1)
+    self.deck.assign_child_resource(self.tip_car, track=1)
 
     await self.lh.setup()
     set_tip_tracking(enabled=False)
@@ -2392,11 +2392,11 @@ async def asyncSetUp(self):
 
     self.tip_car = TIP_CAR_480_A00(name="tip carrier")
     self.tip_car[1] = self.tip_rack = hamilton_96_tiprack_300uL_filter(name="tip_rack_01")
-    self.deck.assign_child_resource(self.tip_car, rails=1)
+    self.deck.assign_child_resource(self.tip_car, track=1)
 
     self.plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     self.plt_car[0] = self.plate = cor_96_wellplate_360uL_Fb(name="plate_01")
-    self.deck.assign_child_resource(self.plt_car, rails=9)
+    self.deck.assign_child_resource(self.plt_car, track=9)
 
     self.STAR._num_channels = 8
     self.STAR._machine_conf = _DEFAULT_MACHINE_CONFIGURATION
@@ -2615,11 +2615,11 @@ async def asyncSetUp(self):
 
     self.tip_car = TIP_CAR_480_A00(name="tip carrier")
     self.tip_car[1] = self.tip_rack = hamilton_96_tiprack_300uL_filter(name="tip_rack_01")
-    self.deck.assign_child_resource(self.tip_car, rails=1)
+    self.deck.assign_child_resource(self.tip_car, track=1)
 
     self.plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     self.plt_car[0] = self.plate = cor_96_wellplate_360uL_Fb(name="plate_01")
-    self.deck.assign_child_resource(self.plt_car, rails=9)
+    self.deck.assign_child_resource(self.plt_car, track=9)
 
     await self.lh.setup()
 
diff --git a/pylabrobot/legacy/liquid_handling/backends/hamilton/nimbus_backend_tests.py b/pylabrobot/legacy/liquid_handling/backends/hamilton/nimbus_backend_tests.py
index ecf883f65a7..6a5060d7850 100644
--- a/pylabrobot/legacy/liquid_handling/backends/hamilton/nimbus_backend_tests.py
+++ b/pylabrobot/legacy/liquid_handling/backends/hamilton/nimbus_backend_tests.py
@@ -699,10 +699,10 @@ async def asyncSetUp(self):
     self.backend.send_command = self.mock_send  # type: ignore[method-assign]
 
     self.tip_rack = hamilton_96_tiprack_300uL("tip_rack")
-    self.deck.assign_child_resource(self.tip_rack, rails=1)
+    self.deck.assign_child_resource(self.tip_rack, track=1)
 
     self.plate = cor_96_wellplate_360uL_Fb("plate")
-    self.deck.assign_child_resource(self.plate, rails=10)
+    self.deck.assign_child_resource(self.plate, track=10)
 
     self.tip = HamiltonTip(
       name="test_tip",
@@ -1083,7 +1083,7 @@ async def test_10uL_tips(self):
     from pylabrobot.resources.hamilton.tip_racks import hamilton_96_tiprack_10uL
 
     tip_rack = hamilton_96_tiprack_10uL("tips")
-    self.deck.assign_child_resource(tip_rack, rails=1)
+    self.deck.assign_child_resource(tip_rack, track=1)
     tip_spot = tip_rack.get_item("A1")
     tip = tip_spot.get_tip()
 
@@ -1110,7 +1110,7 @@ async def test_50uL_tips(self):
     from pylabrobot.resources.hamilton.tip_racks import hamilton_96_tiprack_50uL
 
     tip_rack = hamilton_96_tiprack_50uL("tips")
-    self.deck.assign_child_resource(tip_rack, rails=1)
+    self.deck.assign_child_resource(tip_rack, track=1)
     tip_spot = tip_rack.get_item("A1")
     tip = tip_spot.get_tip()
 
@@ -1137,7 +1137,7 @@ async def test_300uL_tips(self):
     from pylabrobot.resources.hamilton.tip_racks import hamilton_96_tiprack_300uL
 
     tip_rack = hamilton_96_tiprack_300uL("tips")
-    self.deck.assign_child_resource(tip_rack, rails=1)
+    self.deck.assign_child_resource(tip_rack, track=1)
     tip_spot = tip_rack.get_item("A1")
     tip = tip_spot.get_tip()
 
@@ -1164,7 +1164,7 @@ async def test_1000uL_tips(self):
     from pylabrobot.resources.hamilton.tip_racks import hamilton_96_tiprack_1000uL
 
     tip_rack = hamilton_96_tiprack_1000uL("tips")
-    self.deck.assign_child_resource(tip_rack, rails=1)
+    self.deck.assign_child_resource(tip_rack, track=1)
     tip_spot = tip_rack.get_item("A1")
     tip = tip_spot.get_tip()
 
diff --git a/pylabrobot/legacy/liquid_handling/backends/hamilton/vantage_tests.py b/pylabrobot/legacy/liquid_handling/backends/hamilton/vantage_tests.py
index ca3209b395b..957db9c49c9 100644
--- a/pylabrobot/legacy/liquid_handling/backends/hamilton/vantage_tests.py
+++ b/pylabrobot/legacy/liquid_handling/backends/hamilton/vantage_tests.py
@@ -252,12 +252,12 @@ async def asyncSetUp(self):
     self.tip_car = TIP_CAR_480_A00(name="tip carrier")
     self.tip_car[0] = self.tip_rack = hamilton_96_tiprack_1000uL(name="tip_rack_01")
     self.tip_car[1] = self.small_tip_rack = hamilton_96_tiprack_10uL(name="tip_rack_02")
-    self.deck.assign_child_resource(self.tip_car, rails=18)
+    self.deck.assign_child_resource(self.tip_car, track=18)
 
     self.plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     self.plt_car[0] = self.plate = cor_96_wellplate_360uL_Fb(name="plate_01")
     self.plt_car[1] = self.other_plate = cor_96_wellplate_360uL_Fb(name="plate_02")
-    self.deck.assign_child_resource(self.plt_car, rails=24)
+    self.deck.assign_child_resource(self.plt_car, track=24)
 
     self.maxDiff = None
 
@@ -584,7 +584,7 @@ async def asyncSetUp(self):
     self.lh = LiquidHandler(self.backend, deck=self.deck)
 
     self.tip_car = TIP_CAR_480_A00(name="tip_carrier")
-    self.deck.assign_child_resource(self.tip_car, rails=18)
+    self.deck.assign_child_resource(self.tip_car, track=18)
 
     await self.lh.setup()
     set_tip_tracking(enabled=False)
diff --git a/pylabrobot/legacy/liquid_handling/backends/serializing_backend_tests.py b/pylabrobot/legacy/liquid_handling/backends/serializing_backend_tests.py
index 833ac238c8a..c99703d7b6f 100644
--- a/pylabrobot/legacy/liquid_handling/backends/serializing_backend_tests.py
+++ b/pylabrobot/legacy/liquid_handling/backends/serializing_backend_tests.py
@@ -34,12 +34,12 @@ async def asyncSetUp(self) -> None:
 
     self.tip_car = TIP_CAR_480_A00(name="tip carrier")
     self.tip_car[0] = self.tip_rack = hamilton_96_tiprack_300uL_filter(name="tip_rack_01")
-    self.deck.assign_child_resource(self.tip_car, rails=1)
+    self.deck.assign_child_resource(self.tip_car, track=1)
 
     self.plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     self.plt_car[0] = self.plate = cor_96_wellplate_360uL_Fb(name="plate_01")
     self.plt_car[1] = self.other_plate = cor_96_wellplate_360uL_Fb(name="plate_02")
-    self.deck.assign_child_resource(self.plt_car, rails=9)
+    self.deck.assign_child_resource(self.plt_car, track=9)
 
     self.backend.send_command.reset_mock()
 
diff --git a/pylabrobot/legacy/liquid_handling/liquid_handler_tests.py b/pylabrobot/legacy/liquid_handling/liquid_handler_tests.py
index 0a7f6c563e2..03b6087bcf9 100644
--- a/pylabrobot/legacy/liquid_handling/liquid_handler_tests.py
+++ b/pylabrobot/legacy/liquid_handling/liquid_handler_tests.py
@@ -134,37 +134,37 @@ def test_resource_assignment(self):
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="aspiration plate")
     plt_car[2] = cor_96_wellplate_360uL_Fb(name="dispense plate")
 
-    self.deck.assign_child_resource(tip_car, rails=1)
-    self.deck.assign_child_resource(plt_car, rails=21)
+    self.deck.assign_child_resource(tip_car, track=1)
+    self.deck.assign_child_resource(plt_car, track=21)
 
     # Test placing a carrier at a location where another carrier is located.
     with self.assertRaises(ValueError):
       dbl_plt_car_1 = PLT_CAR_L5AC_A00(name="double placed carrier 1")
-      self.deck.assign_child_resource(dbl_plt_car_1, rails=1)
+      self.deck.assign_child_resource(dbl_plt_car_1, track=1)
 
     with self.assertRaises(ValueError):
       dbl_plt_car_2 = PLT_CAR_L5AC_A00(name="double placed carrier 2")
-      self.deck.assign_child_resource(dbl_plt_car_2, rails=2)
+      self.deck.assign_child_resource(dbl_plt_car_2, track=2)
 
     with self.assertRaises(ValueError):
       dbl_plt_car_3 = PLT_CAR_L5AC_A00(name="double placed carrier 3")
-      self.deck.assign_child_resource(dbl_plt_car_3, rails=20)
+      self.deck.assign_child_resource(dbl_plt_car_3, track=20)
 
     # Test invalid rails.
     with self.assertRaises(ValueError):
-      self.deck.assign_child_resource(plt_car, rails=-1)
+      self.deck.assign_child_resource(plt_car, track=-1)
     with self.assertRaises(ValueError):
-      self.deck.assign_child_resource(plt_car, rails=42)
+      self.deck.assign_child_resource(plt_car, track=42)
     with self.assertRaises(ValueError):
-      self.deck.assign_child_resource(plt_car, rails=27)
+      self.deck.assign_child_resource(plt_car, track=27)
 
   def test_get_resource(self):
     tip_car = TIP_CAR_480_A00(name="tip_carrier")
     tip_car[0] = hamilton_96_tiprack_300uL_filter(name="tip_rack_01")
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="aspiration plate")
-    self.deck.assign_child_resource(tip_car, rails=1)
-    self.deck.assign_child_resource(plt_car, rails=10)
+    self.deck.assign_child_resource(tip_car, track=1)
+    self.deck.assign_child_resource(plt_car, track=10)
 
     # Get resource.
     self.assertEqual(self.lh.deck.get_resource("tip_carrier").name, "tip_carrier")
@@ -199,8 +199,8 @@ def test_subcoordinates(self):
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="aspiration plate")
     plt_car[2] = cor_96_wellplate_360uL_Fb(name="dispense plate")
-    self.deck.assign_child_resource(tip_car, rails=1)
-    self.deck.assign_child_resource(plt_car, rails=10)
+    self.deck.assign_child_resource(tip_car, track=1)
+    self.deck.assign_child_resource(plt_car, track=10)
 
     # Rails 10 should be left of rails 1.
     self.assertGreater(
@@ -246,9 +246,9 @@ def test_illegal_subresource_assignment_before(self):
     tip_car[0] = hamilton_96_tiprack_300uL_filter(name="sub")
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="sub")
-    self.deck.assign_child_resource(tip_car, rails=1)
+    self.deck.assign_child_resource(tip_car, track=1)
     with self.assertRaises(ValueError):
-      self.deck.assign_child_resource(plt_car, rails=10)
+      self.deck.assign_child_resource(plt_car, track=10)
 
   def test_illegal_subresource_assignment_after(self):
     # Test assigning subresource with the same name as another resource in another carrier, after
@@ -257,15 +257,15 @@ def test_illegal_subresource_assignment_after(self):
     tip_car[0] = hamilton_96_tiprack_300uL_filter(name="sub")
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="ok")
-    self.deck.assign_child_resource(tip_car, rails=1)
-    self.deck.assign_child_resource(plt_car, rails=10)
+    self.deck.assign_child_resource(tip_car, track=1)
+    self.deck.assign_child_resource(plt_car, track=10)
     with self.assertRaises(ValueError):
       plt_car[1] = cor_96_wellplate_360uL_Fb(name="sub")
 
   async def test_move_plate_to_site(self):
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = plate = cor_96_wellplate_360uL_Fb(name="plate")
-    self.deck.assign_child_resource(plt_car, rails=21)
+    self.deck.assign_child_resource(plt_car, track=21)
 
     await self.lh.move_plate(plate, plt_car[2])
     self.assertIsNotNone(plt_car[2].resource)
@@ -279,7 +279,7 @@ async def test_move_plate_to_site(self):
   async def test_move_plate_free(self):
     plt_car = PLT_CAR_L5AC_A00(name="plate carrier")
     plt_car[0] = plate = cor_96_wellplate_360uL_Fb(name="plate")
-    self.deck.assign_child_resource(plt_car, rails=1)
+    self.deck.assign_child_resource(plt_car, track=1)
 
     await self.lh.move_plate(plate, Coordinate(1000, 1000, 1000))
     self.assertIsNotNone(self.lh.deck.get_resource("plate"))
diff --git a/pylabrobot/legacy/plate_reading/byonoy/byonoy_tests.py b/pylabrobot/legacy/plate_reading/byonoy/byonoy_tests.py
index fc9eddd08c5..fcede101676 100644
--- a/pylabrobot/legacy/plate_reading/byonoy/byonoy_tests.py
+++ b/pylabrobot/legacy/plate_reading/byonoy/byonoy_tests.py
@@ -18,7 +18,7 @@ async def asyncSetUp(self):
     self.lh = LiquidHandler(deck=self.deck, backend=unittest.mock.Mock(spec=LiquidHandlerBackend))
     self.plate_carrier = PLT_CAR_L5_DWP(name="plate_carrier")
     self.plate_carrier[1] = self.adapter
-    self.deck.assign_child_resource(self.plate_carrier, rails=28)
+    self.deck.assign_child_resource(self.plate_carrier, track=28)
     self.adapter.assign_child_resource(self.reader)
     self.plate_carrier[2] = self.plate = cellvis_96_wellplate_350uL_Fb(name="plate")
 
diff --git a/pylabrobot/resources/hamilton/hamilton_deck_tests.py b/pylabrobot/resources/hamilton/hamilton_deck_tests.py
index c2d179421be..9aa0a8b68ed 100644
--- a/pylabrobot/resources/hamilton/hamilton_deck_tests.py
+++ b/pylabrobot/resources/hamilton/hamilton_deck_tests.py
@@ -1,13 +1,16 @@
 import textwrap
 import unittest
+from typing import cast
 
-from pylabrobot.resources import Deck, TipRack
+from pylabrobot.resources import Coordinate, Deck, Resource, TipRack
 from pylabrobot.resources.corning import (
   cor_96_wellplate_360uL_Fb,
 )
 from pylabrobot.resources.hamilton import (
   PLT_CAR_L5AC_A00,
   TIP_CAR_480_A00,
+  HamiltonDeck,
+  STARDeck,
   STARLetDeck,
   hamilton_96_tiprack_300uL_filter,
   hamilton_96_tiprack_1000uL_filter,
@@ -18,6 +21,75 @@
 
 
 class HamiltonDeckTests(unittest.TestCase):
+  def test_rails_is_deprecated(self):
+    """`rails` still places a resource, and says it is deprecated."""
+    deck = STARLetDeck()
+    with self.assertWarns(DeprecationWarning):
+      deck.assign_child_resource(TIP_CAR_480_A00(name="tip_carrier"), rails=1)
+    self.assertEqual(
+      deck.get_resource("tip_carrier").get_location_wrt(deck).x,
+      deck.track_to_location(1).x,
+    )
+
+  def test_track_and_rails_together_is_refused(self):
+    """Passing both is a mistake rather than a preference."""
+    deck = STARLetDeck()
+    with self.assertRaises(ValueError):
+      deck.assign_child_resource(TIP_CAR_480_A00(name="tip_carrier"), track=1, rails=1)
+
+  def test_num_tracks_and_num_rails_together_is_refused(self):
+    class OwnDeck(HamiltonDeck):
+      def track_to_location(self, track: int) -> Coordinate:
+        return Coordinate(100.0 + (track - 1) * 22.5, 63, 100)
+
+    with self.assertRaises(ValueError):
+      OwnDeck(num_tracks=30, num_rails=30, size_x=1000, size_y=600, size_z=300)
+
+  def test_a_deck_saved_with_num_rails_loads_with_the_tracks_it_has(self):
+    """A saved STAR deck counted two more rails than it has tracks."""
+    for factory, tracks in ((STARLetDeck, 30), (STARDeck, 54)):
+      data = factory().serialize()
+      data["num_rails"] = data.pop("num_tracks") + 2
+      with self.assertWarns(DeprecationWarning):
+        deck = Deck.deserialize(data)
+      self.assertEqual(cast(HamiltonDeck, deck).num_tracks, tracks)
+
+  def test_num_rails_counts_as_it_did(self):
+    with self.assertWarns(DeprecationWarning):
+      self.assertEqual((STARLetDeck().num_rails, STARDeck().num_rails), (32, 56))
+
+  def test_rails_is_bounded_as_it_was_and_track_by_the_tracks(self):
+    deck = STARLetDeck()
+    with self.assertWarns(DeprecationWarning):
+      deck.assign_child_resource(Resource("front", size_x=20, size_y=20, size_z=20), rails=32)
+    with self.assertRaises(ValueError):
+      deck.assign_child_resource(Resource("front_2", size_x=20, size_y=20, size_z=20), track=32)
+
+  def test_hamilton_deck_takes_its_track_count_first_as_it_took_rails(self):
+    class OwnDeck(HamiltonDeck):
+      def track_to_location(self, track: int) -> Coordinate:
+        return Coordinate(100.0 + (track - 1) * 22.5, 63, 100)
+
+    deck = OwnDeck(30, 1000, 600, 300)
+    self.assertEqual((deck.num_tracks, deck.get_size_x()), (30, 1000))
+
+  def test_a_deck_implementing_rails_to_location_still_places_by_track(self):
+    class RailsDeck(HamiltonDeck):
+      def rails_to_location(self, rails: int) -> Coordinate:
+        return Coordinate(100.0 + (rails - 1) * 22.5, 63, 100)
+
+    deck = RailsDeck(30, 1000, 600, 300)
+    self.assertEqual(deck.track_to_location(3), Coordinate(145.0, 63, 100))
+    deck.assign_child_resource(TIP_CAR_480_A00(name="tip_carrier"), track=3)
+    self.assertEqual(deck.get_resource("tip_carrier").location, Coordinate(145.0, 63, 100))
+
+  def test_a_deck_implementing_neither_location_method_is_refused(self):
+    class NoTracksDeck(HamiltonDeck):
+      pass
+
+    with self.assertRaises(TypeError):
+      NoTracksDeck(30, 1000, 600, 300)
+
   """Tests for the HamiltonDeck class."""
 
   def build_layout(self):
@@ -33,8 +105,8 @@ def build_layout(self):
     plt_car[0] = cor_96_wellplate_360uL_Fb(name="aspiration plate")
     plt_car[2] = cor_96_wellplate_360uL_Fb(name="dispense plate")
 
-    deck.assign_child_resource(tip_car, rails=1)
-    deck.assign_child_resource(plt_car, rails=21)
+    deck.assign_child_resource(tip_car, track=1)
+    deck.assign_child_resource(plt_car, track=21)
 
     return deck
 
@@ -80,7 +152,7 @@ def test_teaching_rack_excluded_by_nominal_volume_search(self):
     tip_car = TIP_CAR_480_A00(name="tip_carrier")
     for i in range(5):
       tip_car[i] = hamilton_96_tiprack_300uL_filter(name=f"tip_rack_0{i}")
-    deck.assign_child_resource(tip_car, rails=1)
+    deck.assign_child_resource(tip_car, track=1)
 
     tip_racks = [r for r in deck.get_all_children() if isinstance(r, TipRack)]
     matches = [
@@ -122,7 +194,7 @@ def test_assign_gigantic_resource(self):
     stanley_cup = StanleyCup_QUENCHER_FLOWSTATE_TUMBLER(name="HUGE")
     deck = STARLetDeck()
     with self.assertLogs("pylabrobot") as log:
-      deck.assign_child_resource(stanley_cup, rails=1)
+      deck.assign_child_resource(stanley_cup, track=1)
     self.assertEqual(
       log.output,
       [
diff --git a/pylabrobot/resources/hamilton/hamilton_decks.py b/pylabrobot/resources/hamilton/hamilton_decks.py
index 9d81dbbf25b..61e03530540 100644
--- a/pylabrobot/resources/hamilton/hamilton_decks.py
+++ b/pylabrobot/resources/hamilton/hamilton_decks.py
@@ -1,7 +1,8 @@
 from __future__ import annotations
 
 import logging
-from abc import ABCMeta, abstractmethod
+import warnings
+from abc import ABCMeta
 from typing import Literal, Optional, cast
 
 from pylabrobot.resources.carrier import ResourceHolder
@@ -15,8 +16,11 @@
 
 logger = logging.getLogger(__name__)
 
+STARLET_NUM_TRACKS = 30
+STAR_NUM_TRACKS = 54
 
 _RAILS_WIDTH = 22.5  # space between rails (mm)
+_TRACK_WIDTH = 22.5  # space between rails (mm)
 
 STARLET_NUM_RAILS = 32
 STARLET_SIZE_X = 1005
@@ -29,9 +33,63 @@
 STAR_SIZE_Z = 900
 
 
+def track_for_x_coordinate(x: float) -> int:
+  """Which track an x coordinate falls on.
+
+  Args:
+    x: the coordinate, in this deck's own frame.
+
+  Returns:
+    The track, counted from 1.
+  """
+  return int((x - 100.0) / _TRACK_WIDTH) + 1
+
+
 def rails_for_x_coordinate(x: float) -> int:
-  """Convert an x coordinate to a rail identifier."""
-  return int((x - 100.0) / _RAILS_WIDTH) + 1
+  """Deprecated. Use `track_for_x_coordinate`.
+
+  Args:
+    x: the coordinate, in this deck's own frame.
+
+  Returns:
+    What `track_for_x_coordinate` returns for it.
+  """
+  warnings.warn(
+    "`rails_for_x_coordinate` is deprecated, use `track_for_x_coordinate`: a track is the part of"
+    " the deck, and a rail is part of a carrier.",
+    DeprecationWarning,
+    stacklevel=2,
+  )
+  return track_for_x_coordinate(x)
+
+
+def _resolve_num_tracks(num_tracks: Optional[int], num_rails: Optional[int]) -> int:
+  """The track count, from whichever argument carried it.
+
+  Args:
+    num_tracks: the count.
+    num_rails: the same count under its old name.
+
+  Returns:
+    The count.
+
+  Raises:
+    TypeError: If neither was given.
+    ValueError: If both were given.
+  """
+  if num_tracks is not None:
+    if num_rails is not None:
+      raise ValueError("pass num_tracks, not both num_tracks and num_rails")
+    return num_tracks
+  if num_rails is None:
+    raise TypeError("num_tracks is required")
+  warnings.warn(
+    "`num_rails` is deprecated, use `num_tracks`: a track is the part of the deck, and a rail is"
+    " part of a carrier.",
+    DeprecationWarning,
+    stacklevel=3,
+  )
+  return num_rails
 
 
 class HamiltonDeck(Deck, metaclass=ABCMeta):
@@ -39,14 +97,26 @@ class HamiltonDeck(Deck, metaclass=ABCMeta):
 
   def __init__(
     self,
-    num_rails: int,
-    size_x: float,
-    size_y: float,
-    size_z: float,
+    num_tracks: Optional[int] = None,
+    size_x: Optional[float] = None,
+    size_y: Optional[float] = None,
+    size_z: Optional[float] = None,
     name: str = "deck",
     category: str = "deck",
     origin: Coordinate = Coordinate.zero(),
+    num_rails: Optional[int] = None,
   ):
+    # What `@abstractmethod` refused before either could be left to the other: a deck with neither.
+    if (
+      type(self).track_to_location is HamiltonDeck.track_to_location
+      and type(self).rails_to_location is HamiltonDeck.rails_to_location
+    ):
+      raise TypeError(f"{type(self).__name__} must implement track_to_location")
+
+    # First, where `num_rails` was. Defaulted only so `num_rails=` can be given in its place.
+    if size_x is None or size_y is None or size_z is None:
+      raise TypeError("size_x, size_y and size_z are required")
+
     super().__init__(
       name=name,
       size_x=size_x,
@@ -55,18 +125,59 @@ def __init__(
       category=category,
       origin=origin,
     )
-    self.num_rails = num_rails
+    self.num_tracks = _resolve_num_tracks(num_tracks, num_rails)
     self.register_did_assign_resource_callback(self._check_safe_z_height)
 
-  @abstractmethod
+  def track_to_location(self, track: int) -> Coordinate:
+    """Where a track starts on this deck.
+
+    A subclass implements this, or `rails_to_location` as it did before the rename.
+
+    Args:
+      track: the track, counted from 1.
+
+    Returns:
+      Its position, in this deck's own frame.
+    """
+    return self.rails_to_location(track)
+
   def rails_to_location(self, rails: int) -> Coordinate:
-    """Convert a rail identifier to an absolute (x, y, z) coordinate."""
+    """Deprecated. Use `track_to_location`.
+
+    Args:
+      rails: the track, counted from 1.
+
+    Returns:
+      What `track_to_location` returns for it.
+    """
+    warnings.warn(
+      "`rails_to_location` is deprecated, use `track_to_location`: a track is the part of the deck,"
+      " and a rail is part of a carrier.",
+      DeprecationWarning,
+      stacklevel=2,
+    )
+    return self.track_to_location(rails)
+
+  # STAR decks counted two more rails than they have tracks, which is what `num_rails` said and
+  # what `rails=` placement was bounded by. Kept for those deprecated names only.
+  _rails_beyond_tracks = 0
+
+  @property
+  def num_rails(self) -> int:
+    """Deprecated. Use `num_tracks`, which a STAR deck counts two fewer of."""
+    warnings.warn(
+      "`num_rails` is deprecated, use `num_tracks`: a track is the part of the deck, and a rail is"
+      " part of a carrier.",
+      DeprecationWarning,
+      stacklevel=2,
+    )
+    return self.num_tracks + self._rails_beyond_tracks
 
   def serialize(self) -> dict:
     """Serialize this deck."""
     return {
       **super().serialize(),
-      "num_rails": self.num_rails,
+      "num_tracks": self.num_tracks,
       "with_trash": False,  # data encoded as child. (not very pretty to have this key though...)
       "with_trash96": False,
       "core_grippers": None,  # data encoded as child. (not very pretty to have this key though...)
@@ -111,6 +222,7 @@ def assign_child_resource(
     resource: Resource,
     location: Optional[Coordinate] = None,
     reassign: bool = False,
+    track: Optional[int] = None,
     rails: Optional[int] = None,
     replace=False,
     ignore_collision=False,
@@ -124,20 +236,17 @@ def assign_child_resource(
     be assigned directly to the tip or plate carrier respectively. See TipCarrier and PlateCarrier
     for details.
 
-    Based on the rails argument, the absolute (x, y, z) coordinates will be computed.
+    Given a track, the absolute (x, y, z) coordinates are computed from it.
 
     Args:
       resource: A Resource to assign to this liquid handler.
-      location: The location of the resource relative to the liquid handler. Either rails or
-        location must be `None`, but not both.
+      location: Where to put it, relative to this deck. Either this or `track`, not both.
       reassign: If True, reassign the resource if it is already assigned. If False, raise a
         `ValueError` if the resource is already assigned.
-      rails: The left most real (inclusive) of the deck resource (between and 0-30 for STARLet,
-        max 55 for STAR.) Either rails or location must be None, but not both. 1-index similar to
-        markings on the device, but you can place carriers on 0 as well (left support will not
-        touch a support rail).
-      location: The location of the resource relative to the liquid handler. Either rails or
-        location must be None, but not both.
+      track: The leftmost track the resource covers, counted from 1 as the markings on the device
+        are, and down to -4 for the supports left of the first one. Either this or `location`, not
+        both.
+      rails: Deprecated, use `track`.
       replace: Replace the resource with the same name that was previously assigned, if it exists.
         If a resource is assigned with the same name and replace is False, a ValueError
         will be raised.
@@ -149,8 +258,22 @@ def assign_child_resource(
 
     # TODO: many things here should be moved to Resource and Deck, instead of just STARLetDeck
 
-    if rails is not None and not -4 <= rails <= self.num_rails:
-      raise ValueError(f"Rails must be between -4 and {self.num_rails}.")
+    # `rails=` keeps the bounds it had, so a layout that placed before still places.
+    beyond = 0
+    if rails is not None:
+      if track is not None:
+        raise ValueError("pass track, not both track and rails")
+      warnings.warn(
+        "`rails` is deprecated, use `track`: a track is the part of the deck, and a rail is part"
+        " of a carrier.",
+        DeprecationWarning,
+        stacklevel=2,
+      )
+      track = rails
+      beyond = self._rails_beyond_tracks
+
+    if track is not None and not -4 <= track <= self.num_tracks + beyond:
+      raise ValueError(f"Track must be between -4 and {self.num_tracks + beyond}.")
 
     # Check if resource exists.
     if self.has_resource(resource.name):
@@ -160,12 +283,12 @@ def assign_child_resource(
       else:
         raise ValueError(f"Resource with name '{resource.name}' already defined.")
 
-    if rails is not None:
-      resource_location = self.rails_to_location(rails)
+    if track is not None:
+      resource_location = self.track_to_location(track)
     elif location is not None:
       resource_location = location
     else:
-      raise ValueError("Either rails or location must be provided.")
+      raise ValueError("Either track or location must be provided.")
 
     def should_check_collision(res: Resource) -> bool:
       """Determine if collision detection should be performed for this resource."""
@@ -177,11 +300,11 @@ def should_check_collision(res: Resource) -> bool:
       if resource_location is not None:  # collision detection
         if (
           resource_location.x + resource.get_absolute_size_x()
-          > self.rails_to_location(self.num_rails + 1).x
-          and rails is not None
+          > self.track_to_location(self.num_tracks + 1 + beyond).x
+          and track is not None
         ):
           raise ValueError(
-            f"Resource with width {resource.get_absolute_size_x()} does not fit at rails {rails}."
+            f"Resource with width {resource.get_absolute_size_x()} does not fit at track {track}."
           )
 
         # Check if there is space for this new resource.
@@ -300,7 +423,7 @@ def print_resource_line(resource: Resource, depth=0) -> str:
 
       # Print rail
       if depth == 0:
-        rails = rails_for_x_coordinate(resource.get_location_wrt(self).x)
+        rails = track_for_x_coordinate(resource.get_location_wrt(self).x)
         r_summary += f"({rails})".ljust(rail_column_length)
       else:
         r_summary += " " * rail_column_length
@@ -426,12 +549,14 @@ def hamilton_core_gripper_1000ul_5ml_on_waste() -> HamiltonCoreGrippers:
 class HamiltonSTARDeck(HamiltonDeck):
   """Base class for a Hamilton STAR(let) deck."""
 
+  _rails_beyond_tracks = 2
+
   def __init__(
     self,
-    num_rails: int,
-    size_x: float,
-    size_y: float,
-    size_z: float,
+    num_tracks: Optional[int] = None,
+    size_x: Optional[float] = None,
+    size_y: Optional[float] = None,
+    size_z: Optional[float] = None,
     name="deck",
     category: str = "deck",
     origin: Coordinate = Coordinate.zero(),
@@ -442,14 +567,21 @@ def __init__(
     core_grippers: Optional[
       Literal["1000uL-at-waste", "1000uL-5mL-on-waste"]
     ] = "1000uL-5mL-on-waste",
+    num_rails: Optional[int] = None,
   ) -> None:
     """Create a new STAR(let) deck of the given size.
 
-    `with_trash` and `with_teaching_rack` require `with_waste_block` to be true.
+    `with_trash` and `with_teaching_rack` require `with_waste_block` to be true. `num_rails` is
+    deprecated: it counted two more than `num_tracks`.
     """
 
+    # Defaulted only so a deck saved with `num_rails` can leave out `num_tracks`, which comes first.
+    if size_x is None or size_y is None or size_z is None:
+      raise TypeError("size_x, size_y and size_z are required")
+
     super().__init__(
-      num_rails=num_rails,
+      num_tracks=num_tracks,
+      num_rails=None if num_rails is None else num_rails - self._rails_beyond_tracks,
       size_x=size_x,
       size_y=size_y,
       size_z=size_z,
@@ -470,7 +602,7 @@ def __init__(
       waste_block = Resource(name="waste_block", size_x=30, size_y=445.2, size_z=100)
       self.assign_child_resource(
         waste_block,
-        location=Coordinate(x=self.rails_to_location(self.num_rails - 1).x, y=115.0, z=100),
+        location=Coordinate(x=self.track_to_location(self.num_tracks + 1).x, y=115.0, z=100),
       )
 
       # assign trash area, positioned 25mm to the right of the waste block
@@ -480,7 +612,7 @@ def __init__(
           waste_block_x = self.get_resource("waste_block").get_location_wrt(self).x
         else:
           # Fallback: anchor to the rightmost rail when no waste block is present.
-          waste_block_x = self.rails_to_location(self.num_rails - 1).x
+          waste_block_x = self.track_to_location(self.num_tracks + 1).x
 
         trash_x = waste_block_x + 25
 
@@ -522,13 +654,13 @@ def __init__(
         raise RuntimeError("Teaching rack cannot be created when no waste block is present.")
 
     if core_grippers == "1000uL-at-waste":  # "at waste"
-      x: float = 1338 if num_rails == STAR_NUM_RAILS else 798
+      x: float = 1338 if self.num_tracks == STAR_NUM_TRACKS else 798
       waste_block.assign_child_resource(
         hamilton_core_gripper_1000ul_at_waste(),
         location=Coordinate(x=x, y=105.550 - 26 - 9.5, z=205) - waste_block.location,
       )
     elif core_grippers == "1000uL-5mL-on-waste":  # "on waste"
-      x = 1337.5 if num_rails == STAR_NUM_RAILS else 797.5
+      x = 1337.5 if self.num_tracks == STAR_NUM_TRACKS else 797.5
       waste_block.assign_child_resource(
         hamilton_core_gripper_1000ul_5ml_on_waste(),
         location=Coordinate(x=x, y=125 - 18 - 21.5, z=205) - waste_block.location,
@@ -542,8 +674,8 @@ def serialize(self) -> dict:
       "core_grippers": None,  # data encoded as child. (not very pretty to have this key though...)
     }
 
-  def rails_to_location(self, rails: int) -> Coordinate:
-    x = 100.0 + (rails - 1) * _RAILS_WIDTH
+  def track_to_location(self, track: int) -> Coordinate:
+    x = 100.0 + (track - 1) * _TRACK_WIDTH
     return Coordinate(x=x, y=63, z=100)
 
   def get_trash_area96(self) -> Trash:
@@ -580,7 +712,7 @@ def STARLetDeck(
   """
 
   return HamiltonSTARDeck(
-    num_rails=STARLET_NUM_RAILS,
+    num_tracks=30,
     size_x=STARLET_SIZE_X,
     size_y=STARLET_SIZE_Y,
     size_z=STARLET_SIZE_Z,
@@ -607,7 +739,7 @@ def STARDeck(
   """
 
   return HamiltonSTARDeck(
-    num_rails=STAR_NUM_RAILS,
+    num_tracks=54,
     size_x=STAR_SIZE_X,
     size_y=STAR_SIZE_Y,
     size_z=STAR_SIZE_Z,
diff --git a/pylabrobot/resources/hamilton/nimbus_decks.py b/pylabrobot/resources/hamilton/nimbus_decks.py
index 00b90c2cbac..9794cb35bd1 100644
--- a/pylabrobot/resources/hamilton/nimbus_decks.py
+++ b/pylabrobot/resources/hamilton/nimbus_decks.py
@@ -70,7 +70,7 @@ def __init__(
             creates a waste block with 8 channel positions. If None, no waste is created.
     """
     super().__init__(
-      num_rails=num_rails,
+      num_tracks=num_rails,
       size_x=size_x,
       size_y=size_y,
       size_z=size_z,
@@ -164,21 +164,19 @@ def _create_default_long_waste(self) -> None:
       # Assign waste position to waste block
       waste_block.assign_child_resource(waste_position, location=pos_plr_rel)
 
-  def rails_to_location(self, rails: int) -> Coordinate:
-    """Convert a rail identifier to an absolute (x, y, z) coordinate.
+  def track_to_location(self, track: int) -> Coordinate:
+    """Where a track starts on this deck.
 
-    Converts rail number (1-30) to PyLabRobot coordinates. Internally maps
-    hardware tracks to API rails for consistency with other Hamilton decks.
-    Uses instance attributes for rail positions, which can be set from config files.
+    Read from instance attributes, which can be set from config files.
 
     Args:
-        rails: Rail number (1-30, maps to hardware tracks)
+        track: the track, counted from 1.
 
     Returns:
-        PyLabRobot coordinate relative to deck origin
+        Its position, in this deck's own frame.
     """
     # Calculate X position in Hamilton coordinates using instance attributes
-    x_hamilton = self._rail_start_x + (rails - 1) * self._rail_width
+    x_hamilton = self._rail_start_x + (track - 1) * self._rail_width
     y_hamilton = self._rail_y
     z_hamilton = 0.0
 
diff --git a/pylabrobot/resources/hamilton/vantage_decks.py b/pylabrobot/resources/hamilton/vantage_decks.py
index 01797975a69..9f338046e72 100644
--- a/pylabrobot/resources/hamilton/vantage_decks.py
+++ b/pylabrobot/resources/hamilton/vantage_decks.py
@@ -1,6 +1,6 @@
 from pylabrobot.resources.coordinate import Coordinate
 from pylabrobot.resources.hamilton.hamilton_decks import (
-  _RAILS_WIDTH,
+  _TRACK_WIDTH,
   HamiltonDeck,
 )
 from pylabrobot.resources.trash import Trash
@@ -31,7 +31,7 @@ def __init__(
       # the HxConfigEditor.
       size_x = 1237.5
       super().__init__(
-        num_rails=54,
+        num_tracks=54,
         size_x=size_x,
         size_y=653.5,
         size_z=900.0,
@@ -54,8 +54,8 @@ def __init__(
     else:
       raise ValueError(f"Invalid deck size: {size}")
 
-  def rails_to_location(self, rails: int) -> Coordinate:
-    x = 32.5 + (rails - 1) * _RAILS_WIDTH
+  def track_to_location(self, track: int) -> Coordinate:
+    x = 32.5 + (track - 1) * _TRACK_WIDTH
     return Coordinate(x=x, y=63, z=100)
 
   def serialize(self) -> dict: