Piston Sizing

[Bob Culver]

You have to recheck with them locked. As above can acheive the same with filed nails held by a clothespeg. If file a thou short can stretch by hammering the middle. 
Care is necessary transferring to external mic as the ratchet stop reading is slightly different from static.
It is quite diffivult to find the exact max wear in old cyls and I often wonder just how much hunting for guidelines presume.
On old engines and esp Sevens piston clearnce including wear, and rock seem to lead to top ring vertical wear, much reduced in moderns