Profile and datum B

[[An...]]

See attached.

(E.o.T.)

Pic_4-38.pdf

[[Aa...]]

And for our weekly picking apart of a figure from the standard...

Turns out I agree with you. The datum B reference in the DRF of the three FCFs you've highlighted is completely unnecessary. Referencing this figure, 4.8 says "A datum feature is selected on the basis of its functional relationship to the toleranced feature and the requirements of the design." This is not that. The translational constraints added by the inclusion of a datum B reference is inconsequential to the profile controls applied to the planar faces in question.

[[Aa...]]

I need to retract that statement. The position and profile controls in this figure all reference the same datums in the same order of precedence, making them all simultaneous requirements. This would be insignificant except in cases where the datum feature A was unstable. If they were separate requirements, a different candidate datum A could be selected for each.

However, as the standard is not highlighting this point, it does seem that the inclusion of B in those FCFs in this figure did nothing to enhance the illustrating power of this figure, and only added confusion.