JusCalc.

A calculator with no buttons. Every input is a drag.

⬇ Download the latest APK

TL;DR

The problem: phone calculators are grids of tiny buttons designed for a mouse finger. One-handed, on the move, you mistype.

The solution: JusCalc replaces buttons with drag strips. Numbers live on two rotary dials — flick and release on your digit. Selections chase your finger, detent haptics tick, springs settle. No aiming, no mistypes.

Why JusCalc?

	What it does
No buttons	Every input is a drag or tap — usable one-handed, eyes half-open
Two ways to count	Rotary dials, or Number-dots mode: both bars become one 1–10 counter
Speaks results	55000 → 55 THOUSAND, 1200000 → 1.2 MILLION
Remembers	Pull-down history survives restarts; tap a row to keep calculating
Dresses up	Six colorways: Olive, Cherry, Vanilla, Violet, Turquoise, Lavender
Offline	Zero network permission — your calculations never leave the phone

Gestures

Control	Drag left	Drag right	Tap
Top dial (5–9)	higher digit	lower digit	nearest third
Bottom dial (0–4)	higher digit	lower digit	nearest third
Dots (both bars)	slide across — lit count = digit (10 → 0)	continues into the other row	dot's position
( ) pad	pick from the ( ) row	—	smart paren
X pad	×	÷ (or up through ÷ × + −)	×
AC • pill	•	AC	either half
Del = pill	=	Del	either half

Display: tap copies (result after =, expression while typing) · hold opens settings · pull down reveals history. Back closes settings, then history, then the app.

How JusCalc compares

	JusCalc	Stock calculator	Scientific apps
Button-free input	✅ everything drags	❌	❌
One-handed use	✅	⚠️ big phones, no	⚠️
Word-spelled results	✅ 1.2 MILLION	❌ 1200000	❌
Persistent history	✅ on-device	⚠️ varies	✅
Scientific functions	❌ (basic + parens)	❌	✅
Price / ads / tracking	✅ free, none, none	✅	⚠️ often ad-supported

Use JusCalc for everyday arithmetic with one thumb. Use something else for trig and logarithms.

Installation

The APK (recommended)

Grab it from Releases (Android 7.0+). Coming from v1.0? Uninstall it first — v1.0.1 switched signatures.

From source

git clone git@github.com:shubh72010/JusCalc.git
cd JusCalc
./gradlew :app:installRelease   # or :app:installDebug

Requires Android SDK 37 + JDK 17.

For developers

./gradlew :app:assembleDebug       # debug APK
./gradlew :app:assembleRelease     # upload-signed release APK
./gradlew :app:testDebugUnitTest   # unit tests (CalcEngineTest must stay green)
./gradlew :app:lintRelease         # must be 0 errors before any release

Push a v* tag and CI tests, builds, and publishes the APK to a GitHub Release with build provenance.

┌──────────────────────────────────────────────┐
│ MainActivity.kt — all UI + state             │
│  Display · Dials · Dots · Pills · Pads       │
│  HistoryPanel · SettingsSheet                │
└──────────────────────┬───────────────────────┘
                       │ expr / = 
                       ▼
┌──────────────────────────────────────────────┐
│ CalcEngine.kt — EvalEx (BigDecimal, 12-digit)│
│  evaluate() → Ok | Err · numberToCompact()   │
└──────────────────────┬───────────────────────┘
                       │ persist (30 cap)
                       ▼
              SharedPreferences

More: ARCHITECTURE.md · DESIGN_LANGUAGE.md · AGENTS.md

Troubleshooting

"App not installed" when updating from v1.0

v1.0 was debug-signed, v1.0.1 uses the upload key — Android treats them as different apps. Uninstall v1.0 first (its history goes with it).

adb: more than one device/emulator

The network exposes the device twice. Pin every call:

export ANDROID_SERIAL=192.168.1.39:39585

Build fails on missing SDK 37

Install Android SDK Platform 37 via SDK Manager (sdkmanager "platforms;android-37"), then rebuild.

Limitations

• Basic arithmetic only — + − × ÷, parens, decimals. No trig, logs, or matrices.
• 28-character expressions, 30-entry history — caps, not bugs.
• Phone-first layout — no dedicated landscape/tablet arrangement.
• ~8 MB APK — R8/minify is off; size work hasn't mattered yet.

FAQ

Is it offline?

Fully. No network permission in the manifest — nothing leaves your phone.

Where is my history stored?

On-device SharedPreferences, one line per entry. Uninstalling clears it; updates keep it.

Will it come to the Play Store?

The upload key is ready — that's the main blocker gone. Store listing is still to do.

Why EvalEx instead of hand-rolled parsing?

BigDecimal math with correct precedence for free, no scripting engine, and anything it rejects becomes a clean ERROR. Less code, fewer bugs.

Credits

• Math: EvalEx (Apache-2.0)
• Geometry: Kyant0/Shapes
• Typeface: Geist (OFL), bundled in res/font