[BillA]

both Colin and Nevin will be happy to speak with you, good people

don't understand the difficulty, 'anything' can be tested now
I'm commenting on assumptions, who (other than I) has looked at flatness wrt wb testing ?

before you get too far into flatness characterization and subsequent calcs best see what data you are going to have to work with
??

BTW, laser interferometers are better for the quantification of flatness
(I'm not clever enough to build one, don't have the bucks to buy one)

BTW, it is unnecessary to reproduce each post; only you and I are posting, I can follow what you are saying

EDIT
no, one does not 'quantify' a worst case by making an assumption re its magnitude
"to make sure we do better" is a mfgr activity, the tester is concerned with the DUT and its characterization
I'm talking about testing, not the analysis of process variation and defining a 'lower' process limit for mfgn
the tester does not have a clue about such (assuming that it was defined by the mfgr) w/o a very large set of samples over a number of production lots
no 'outside' tester will ever have access to a sufficient quantity of pieces (or the time !) to define the process variation, a test is a window