This 7/8” optically clear gauge is used to set damper timing based on 1 ¾” hammer blow distance. Strong rare-earth magnets attach the gauge firmly to the strings just above the dampers. Using a damper spoon regulator to adjust the spoons, you can visually sight through the gauge to watch the result of your timing adjustments. Posture is better, and you might find the job a bit quicker, with accuracy that you can see.