"Surface Plate" Workbench

[Toolmaker51]

top within a tolerance of .010" overall and less than .005" in smaller areas certainly acceptable for lots of work.......but if you'd care to improve that down the road, supporting by the Airy Points with [could] reduce it to a minimum. If adjustments proved to reduce it when built, I'm convinced Airy calculations will be successful.
https://en.wikipedia.org/wiki/Airy_points