So what do you think your system is capable of resolving 1/2 a thou of an inch or better ? Does it allows you to get the surface genuinely coplanar ? I notice it indicates tilt in the graphic.

A cheap Chinese granite surface plate is an excellent investment.I got a class b 12x18x3 inch here in New Zealand delivered for less than $120NZ.Class b is any two points no more than 2/10000 difference.

I recall reading about H-BCAM when its been raised before.Just done another quick skim over it.But "quite easy" wasnt a phrase I would apply to it !!! I have seen a simpler hardware only system in Circuit Cellar some years ago.
Great to see you have a successful system.Sounds like some of your available parts might differ from the average available workshop cast offs though.