Instead of fitting a value linearly, this smoothly interpolates the data
// This will smoothly return a value between 1 to 0 between frames 48 to 155
//fit01(smooth($F, 48,155), 1, 0)
smooth(48, 155, @Frame);
// As opposed to fit($F, 48, 155, 1, 0) which will linearly interpolate these values