Nice! It's good to see apps written for the nook.
The calculator looks nice and the e-ink optimization is great,
however, since I don't have anything to calculate just now
I just did a bit of stress testing to find that:
a) there seems to be an int overflow on really large nubers, it either crashes or warps to negative.
b) I'm not sure what pressing '=' repeatedly is supposed to do (if anything at all) as it gives weird and inconsistent results.
c) it crashes on division by zero (I HAD to try that
d) Also, to have a useful division function you really need to use floating point numbers.
It's a nice project, but needs some working on before being a useful calculator