For those who might want to put this in, but don't really know how to program the calculator, I thought I'd post where some of the keys are located to save people some time. (This is for the TI-83's. I don't own a TI-89, so I don't know anything about them. :P )Disp and Input are under PRGM -> I/OLbl is under PRGM -> CTLY1 is under VARS -> Y-VARS -> FUNCTION--> is the STO-> keynDeriv is under MATH -> MATH= and < , I could only find under CATALOG (2nd + 0). Just hit the Z button and scroll down until you find them.The rest of the variables are just any letters you put in using the ALPHA key (or A-LOCK)
Neat! Looks like a handy program.