On 2011-06-15, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
"T.Alan Kraus" fired this volley in news:4df8d9c2$0
:

I don't like that, because it relies on two separate indicators, and
that introduces uncertainty as to their mutual adjustment an reading.

Nope. Just turn it 180 degrees to check any reading.

This is a good point. Well, I did it with one indicator, just because
I did not have this fancy one. I used top of the Kurt vise as a
reference surface.