You trust a dial indicator to measure gear backlash,, the probe moves a precision rack, which turns a precision gear, and moves a precision needle,, you trust it to measure 4 - 8 thousands of an inch.(distance),, You trust a dial indicator probe to move a precision rack, to turn a precision gear , that moves a precision needle to indicate when a lifter is at .050 lift, - not .049, - not .051, but precisely .050..(distance), - as a foundation for your cam set-up.. You trust a dial indicator yada yada to measure .002 transmission freeplay ..(distance)
Yet you put the same dial indicator,, it's presicion needle, precision gear, on a similar precision rack, that's 4 - 5 inches long,, call it a vernier caliper,, and you deem it's not accurate enuff to compare a .005 diff on 2 different shaft diameters..(distance)..
If you believe this, Give your head a shake,, cuz your logic and common sense,, need a reboot.. imho
Matching pistons to bores, rods to journals,, working in 10 thousands of an inch, - I use a mic,, searching thru my shim collection,, or going to a pipe shop,, caliper is close enuff, cuz I'm not taking a mic to a pipe shop unless I'm searching for precision..
hope it helps