Return an exact answer on the home screen.

[Tim Wessman]

What will most likely happen at some point is the a b/c key will ALSO cycle through as one of the options a QPI (that program) variant which will match values of sqrt, pi, etc. Right now it cycles decimal, fraction, mixed fraction, <insert qpi>, then back to decimal.

I also think it would be a good ideat extend that to let you toggle representations in other screens as well. Grapher, num table, etc.