My Comp 4930 Beehive Valve Spring Height Micrometer does not directly read installed spring height. It is calibrated to read the micrometer’s overall height rather than the recessed face where the retainer rests. To determine the correct spring height you need to subtract the depth of the recessed area. It is difficult to accurately measure that depth (approximately 0.140 inch). I also have a set of Comp 772 Titanium retainers (for beehive springs) that do not fit the bore of the micrometer. The neck of the retainers is 0.640 inch, while the micrometer bore is 0.635 inch. Stock GM retainers do fit.