Hello!
Thanks for enlightning my long-int-problem ... of course some hours of time converted to tenth of seconds exceed the int-boundary.
I'm a HP calculator fan. One of the most powerful traditional RPN calculators is the WP34s. Surprisingly the software doesn't come from HP but is open source made by some HP-lovers (Paul, Walter, Marcus, ...).
My calculator is almost finished and some kind of "poor people's WP34s" with a lot of math functions (trigonometrics, hyperbolics, statistics, normal distribution, regression, conversions, clock, ...). It's based on an arduino (nano) with an excellent OLED-display (128x64) and a selfmade 4x3-keyboard. Right now I'm doing some miniaturizing and providing some additional battery powering.
Of course an arduino is an 8-bit-calculator with 5 to 6 digits accuracy. But that is (in my opinion) really enough to make a scientific calculator. But yes, that's not capable to add billion-numbers with cent-accuracy.
Regards
deetee