Valve spring micrometer

When I run into this scenario I just use 1 keeper and hold it square while I turn it to the measurement. Don't worry about jamming both keepers in there for a measurement. Also when I got mine I turned it to various heights like 1.600" 1.700" 1.800" and actually measured it with calipers. It was .020" larger. I chucked 1 half in the lathe and faced .020" off and now it reads accurately. Just something to check if you haven't already. J.Rob