Useless Position Callout?

[[Jo...]]

Hello All,

Unless I am missing something, I think I have a useless position callout on a print that I'm working on. As shown in the included pic, Datum A is a face and Datum B is the width between the 2 edges perpendicular to -A-. I used symmetry plane to define the width. I think most people would use lines rather than planes for this, but I don't think it should make a difference regarding my question. Symmetry Plane B sets my X origin. So, my question: Is there a point to the Position callout of -B- to -A-? I put a Position Characteristic, chose -B- as my feature, clear DRF, set -A- as my primary Datum. After choosing those, 'Only X' is the only option I have in the 'Shape of Zone' dialogue, which makes sense to me because I don't know what else could be evaluated in this position callout. So, am I missing something or is this just a useless callout on a print?

I think this may be an inexperienced engineer who is used to seeing a cylinder that is perpendicular to a Primary Datum plane called out as a secondary datum with a position callout to that primary datum but doesn't understand why. But again, maybe I am overlooking something.

[[Ke...]]

Symmetry plane is the way to go... I believe that your position result should be similar/equal to a perpendicularity evaluation.

[[Pa...]]

I agree with Keith.  This callout only controls the perpendicularity of the FOS (Centerplane of the rectangular feature).  Any perpendicularity error in either of the two affected planes will contribute to position error; though not always 1 to 1.  The constructed symmetry plane is the correct interpretation.