Rattle your calipers

[mklotz]

Perhaps I am thinking a bit slow this morning. How do you measure the Rattle inside the bore?

Lautard doesn't mention how that was done.

If the "rattling" was done near the mouth of the bore simply holding a scale in place and reading the swing would work. Another way I can imagine would be to use a pair of dividers and keep opening them until their span matched the swing of the stick, then hold them against a scale. Remember, even a poor estimate of the swing will improve the estimate of the bore. A detailed error analysis would be a waste of time; if you really need to know the bore with high accuracy you'll use more sophisticated techniques.