Each key position along a path has: A key value (such as a position) A key fractional time Interpolation fills in values between your key values: Fractional Time Position 0.0 0.0 0.0 0.0 0.1 0.4 0.1 0.0 0.2 0.8 0.2 0.0 . . . . . . 0.5 4.0 1.0 0.0 . . . . . .