Bore gauge with dial indicator

re post *1 Bore gauge with dial indicator. By geniusz K. 11:33 video:
A caveat for when indicators reading an arc. Such a tool is accurate, being comparative. Regardless increments of the dial, will not provide precise measurement of difference to another, such as a sample against part being worked. Discounting fit of pin to hole in lever, the indicator tip will not remain in the same point on the lever as it swings an arc, introducing a sine error.
The same situation arises with test indicators, but they are built to swivel. That provision allows user to orient the most perpendicular relationship between indicator point of contact and part being examined.
Another accommodation, found in high grade test indicators, the arm tip isn't spherical, but as described by manufacturers "pear shaped".

One more manifestation is seen in marksmanship, where placement of the finger and shape of trigger itself work to generate the straightest pull possible. To utilize that they'll exercise with a short dowel between finger tip and heel of hand, any deflection becomes readily visible.

Bore gauge with dial indicator - video