Taks a value and range and returns a smooth interpolation between 0 and 1.
smooth(value, minimum, maximum)
When value is less than minimum, the return value is 0. If value is greater than maximum, the return value is 1.
smooth ($F, 12, 55)
This example will generate an ease-type curve between values 0 and 1, starting at frame 12 and ending at frame 55. Dig it!