This calculator uses a full 16 button matrix keypad. The Arduino deciphers button pushes with the help of the Keypad library, at which time the appropriate character is displayed on the 2×8 LCD ...

[Danko Bertović] wondered the same thing and he built an Arduino with a single button ... calculator for his latest Volos Projects video. You can find the source code online and he used a library ...

Using a CNC machine, the calculator has been constructed using a wooden case together with acrylic screen protector, and a little Arduino hardware ... and light touch buttons are rare.