Chainsaw Repair

He's saying a micrometer is more accurate than your digital caliper. There is a. 0005 variation on the Mitutoyo so it could read .0005 and the true size could be  .001.   Don't think you are gonna have fitment issues with your piston, splitting hairs at this point!! Lol

+1

measuring tools wear or loosen up over time.  when they are still new, i like to measure a guitar pick, and write the measurement on it with a permanent marker.  keep it in a drawer.  this way, you can always go back and measure it again to see if the tool is still reading the same.  a better idea is to use common "feeler guages" like those used to set points for example.

this is good peace of mind if the caliper was dropped on the floor, or starts to show wear marks on the slide or tips.  some low buck calipers are surprisingly accurate.

you can buy "checking standards", but a set of those costs more than an expensive caliper.  some manufactures may offer a service to recalibrate the tool.

0.01 mm is too small of a difference to be concerned about.  at about 0.05 mm,  get questionable with a caliper.

regards
-joe