Put the gage in the bore with the handle off-center. Snug up the screw & pull the contacts over-center "One Time". Finish tightening the screw making certain nothing moves remove gage & measure with a micrometer.

That's how I was taught by old-time machinists who had likely worn out a few sets of them. This has always worked for me & I have checked myself against precision dial bore gages & been extremely consistent with both devices.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra