4. The magnifier comes with two scale glasses, one already fitted and the other in a separate holder. They are identical, except that scale markings are black on one and white on the other. On nearly all club faces the white scale will be easier to read.
5. Rest the clubhead on a table or other surface, so that the club face is horizontal. You may find it helps to rest the club’s shaft on your shoulder or on some raised object, in order to leave both hands free to adjust the magnifier.
Since good light is needed it is helpful, indoors, to place a reading lamp close to the clubhead, preferably shining along the direction of the grooves on the club face. Make sure you hold the magnifier in such a way that your fingers do not obscure the light.
6. Place the magnifier on the club face and look through it. By turning the knurled ring on the eyepiece you should be able to bring into sharp focus both the scale and surface features on the club face. You should also be able to see clearly the bright edges you have scraped on the grooves against the black background.
Notice that the magnifier scale is in thousandths of an inch (or millimetres) and is marked at intervals of 0.005 inches (0.5 mm), except immediately to the right of the long vertical zero line, where the intervals are 0.008 inches (0.2 mm) or 0.004 inches (0.1 mm). You should use this latter part of the scale for the precise measurement of the groove width (See Figure 4).