A view of the lapping compound on the valve seat face.

The compound is finely abrasive; the rotating of the valve via the joystick works the compound between the seating surfaces to smooth and mate the valve to the seat. It is a very slow motion grinding effect. Only a very slight pressure is applied on the valve. The purpose is to let the compound do it's job gently to remove any irregularities between the valve and seat. Patience is a virtue in this endeavor. Usually it will take several times of applying compound; working the joystick; and cleaning off the compound from the valve and seat to see how it is progressing...to get the job right.