I think that flatness of the derived median plane idea was offered in case the max. material modifier in the geometric tolerance window was thought necessary for the design intent of the part. I believe that the quickest way to check the flatness of DMP (at circle M) is with a full form functional gauge (bridge gauge). With the .500 dia. protrusion on the top of the part this inspection might get slightly more costly. It also should be noted that rule #1 does not apply to FDMP.
To learn more about all of these controls/callouts. And to avoid redundant callouts on the drawings.
To see and understand the "unintended consequences" of some GD&T callouts. --direct versus indirect relationship between features---
IF FDMP had been specified and was also called out as a datum feature would the datum be the derived median plane or the center plane? Or are they the same in this instance?
In my hypothetical case I don't have a datum feature (only DMPF and size dimension). Remember: the OP question has been answered and I am building additional or revised constrains and /or questions based on his original thread.
Also what is that "center plane"? (maybe wrong nomenclature) This question has been asked before.
