itch.io

to go backwards it wants you to, using math operations go from a number X to X - 1, and the result can't be zero I think.  I figured out how to do it with 2 operations, but that required being able to enter 2 operations at once.  So it shows what's possible with the current buttons, but not whether the calculator can accept it I think.

I'm stuck on figuring out M-, as i have no idea what I did for M+ even after resetting the game to try and pay attention.

you'd need 14 in a row to hit 1 Billion in a single run, which is a sub 1% chance.  Even 12 in a row is sub 2% and you'd need to get that several times.