"Another cool feature is variable storage. This means you can
set x = 7 and y = 4 and then solve equations such as z =
4*x+5*y^2-17. To delete the value of a stored valuable, click Edit
-> Delete Variable and then select the variable from the list.
Along with these variables, SpeedCrunch also remembers every
expression you ever enter, and you can browse through the history
of expressions by using the up and down arrow keys."