Wiley Horne -- So. Calif.
>Thanks Joel and Darin,

Joel, that answers it. You are saying that in fact one can learn to set the work down on the plate in such a way that even small convexity can be detected. I kinda like your other idea of not getting in that situation in the first place--by forcing a _slight_ concavity.

Darin, I can certainly visualize that spot and scrape is the last thing you do, for fine tuning of a surface you have already gotten 'close'.

Wiley