DumberKit: Calculator

A calculator, unit converter and currency converter for keypad phones like the Qin F21, Dumber Mini or Doov R77 Pro. There are no on-screen buttons: you type the calculation straight on the keypad and press OK for the result. Touch is switched off inside the app, so nothing gets pressed by accident in your pocket.

Keys
• 0–9 – type numbers
• * – add an operator, press it again for the next one (+ − × ÷)
• Hold * – a palette of symbols laid out like the keypad: ^, √, parentheses, %, ±
• # – decimal point
• OK or Call – show the result
• Back – delete the last character; hold it to clear everything
• ↑ / ↓ – go through the history
• ← / → – switch between Calculator, Unit converter, Currency converter and Settings

Features
• The usual order of operations and exact decimals (0.1 + 0.2 = 0.3)
• History like a paper tape, cleared when you close the app
• Unit converter for length, area, volume, mass, temperature, time, speed, pressure and energy, in both directions
• Currency converter with about 30 currencies at the European Central Bank's rates, works offline with the last ones
• Copy the result, or take a converted value over to the calculator
• System, light, dark, dark red and custom themes, a keypad-friendly color picker, blue or any other icon color
• No ads, no tracking; internet only for the ECB's currency rates

Based on Fossify Calculator (GPL-3.0), keypad input inspired by Calc-U-Later.