The BackParamA property is relevant when a part’s
/BasePart/BackSurface is set to Motor or SteppingMotor and
/BasePart/BackSurfaceInput is set to Sin. It determines the amplitude of the motor’s rotational velocity, using the following formula:
MotorVelocity = ParamA * math.sin(workspace.DistributedGameTime * ParamB)
There are no other usages for this property.
This code sample demonstrates how surface properties can be set using only a NormalId (Top, Front, etc). It switches a motor’s -SurfaceInput from NoInput, Constant and Sin to show how each work using -ParamA and -ParamB properties.