wrote in message
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On Mar 25, 9:00 am, "

When I glue something up in the field that requires this kind of
clamping, I actually level my "table" on the sawhorses by carefully
leveling the material I am using for a top.

This cuts out most of the problems.

Level or planar? How level is level? I see vertical glue-up jigs.
How do they work?

When clamping up water boards the surface absolutely myst be "Level".