Online Mercer gauge usage info?
 

I was trying to describe by e-mail to a friend how to use a Mercer bore
comapritor gauge, and then tought that there must be some decent on line
info, maybe with pictures, but a Google search of "Mercer gauge" shows VERY
little info and no instructions. Does anyone have any link to such info, as
my typing speed is really not up to a detailed resume. Thanks