Arduino HP-25 Simulator

[TellyS]

(moved from the Articles Forum, where it was misplaced)

I purchased a couple of 3.5" TFT LCD screens for Arduino some time ago and I was looking for a project for them. I finally decided to replicate the functionality of my very first HP calculator, the HP-25. 2,500 lines of code later I managed to get something that looks like the HP-25 and, for the most part, behaves like an HP-25.



Those TFT screens are not very reliable, so getting a few things to work properly was very hard. If you have 5 minutes to kill, you may want to watch it in action on YouTube:

https://youtu.be/XZgH-pHiQMw

What is not even close to the HP-25, however, is the accuracy of calculations and even the number representations. I relied on Arduino's built-in math library and number handling that is apparently not sufficient. Arduino float/double has a range of 3.4028235E+38 to -3.4028235E+38 and 6-7 decimal digits of precision. The 25 can handle much larger numbers and with greater accuracy. Any suggestions would be appreciated, if there is a solution.