wrote:

And if you are positive that the reference surface is flat...

There is a thread going today about that at:
http://www.practicalmachinist.com/ub...c/30/6548.html

Forrest Addy was writing on how to test for flatness. I have two granites
and work has a bunch of them. I've been planning to set my granites up on
works far larger (and better) granites and sweep mine with my tenths
indicator.

Wes