I saw this set of gauges -

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=5649

Looks like you set the gauge then use a measuring tool on the gauge. Question is, assuming I'm measuring an irregular cylinder, how do I get the gauge out while retaining the setting? Seems I have to disrupt the setting and count turns (lose precision) or risk scratching the cylinder. What am I missing?

Thanks,
Sixto
93 300SD