It may be quite acceptable, for an experienced user of the measuring equipment, to abbreviate the measuring procedure on clubs whose grooves clearly lie well within the specified dimensions.
First, inspect the club face by eye, and check whether the grooves are:
a) unevenly spaced
b) of unequal width
c) unusually wide
d) unusually close together
If any of these conditions apply, then the full measurement must be carried out.
If none of these conditions apply, follow the procedure on the previous page.
IF YOU HAVE ANY DOUBT, CARRY OUT THE FULL MEASUREMENT.
The pre-2010 specifications go on to state:
The depth of a groove must not exceed 0.020 inches (0.508 mm).
In order to help officials rule on groove depth in the field, a simple gauge has been developed which is available from the USGA at a reasonable cost.
The gauge consists of a small rectangular block which has a raised, thin, protruding ridge. This ridge measures exactly 0.022 inches (0.559 mm) in depth, which offers a small tolerance suitable for measurements made in the field.
Method of Use
In order to judge the depth of a groove on a club, the block should be placed onto the face with the ridge running along the inside of the groove. The user should then apply pressure to the block, on both sides of the ridge, to see if the block will rock from side to side.
If the block does noticeably rock, then the groove cannot be too deep. It means that the depth of the ridge is greater that the depth of the groove.
If, on the other hand, the block lies flush with the face and cannot be rocked, it means that the groove is likely to be too deep.
In both instances above, the gauge should be used on at least six grooves within the “impact area” of the face (or near the toe for club faces which are quite worn).
The player should be advised not to use the club in a situation where at least three grooves appear to be too deep when using the gauge.