The tiny “punch mark” , and there is a corresponding one on the moving jaw is to set divider points to a precision dimension. Pretty handy set -up when doing “old school” layout work.
I was just watching some machining videos last night showing how to lay out
a octagon and a hex using a compass / divider. I can see where that old
school caliper with the punch mark for setting the divider would be handy.
Only one question….. why isn’t the punch mark on the “Zero”?