A scientific calculator usually has special buttons for parentheses, trigonometric functions, exponents, inverses and pi -- among other things. A graphing calculator does even more.

Since launching in 2011, Desmos has offered a free online graphing calculator alongside several other tools, like some for geometry.

The Desmos calculator is more advanced than the TI-84 or other devices, offering a friendlier interface, live graphing updates, and free access via a smartphone, tablet or any other connected device.