A cool way to look at functions.
Two number lines are shown, one is for the input x, and the bottom is for the output y. As you slide x along the number line, the output y changes based on the function. The function can be changed by simply typing a new one in. The user can also change how the number lines are scaled. Many options can be hidden. Can be used like a puzzle where the user can't see the function and has to guess it based on how the input/output changes.
