A
Texas Instruments graphing calculator. Basically allows one to get an
A on any test in
high school math, including
calculus if you have even the
slightest idea of what you are doing.
Best part is it can help you speed through anything you already know from
factoring to
limits (it even has an
infinity button) to get to the good
stuff. Considered
unfair by many.
Better than
TI-92 because it doesn't have a
qwerty keyboard so its legal on
SAT,
Academic Decathlon, etc.