Origin related to Pattern

[[To...]]

Just throwing this out for discussion.... Keep the peace.

ASME Y14.5-2009 Para 4.12.3 states "The origin of the datum reference frame MAY be established at the center of the pattern of the datum feature simulator where it intersects plane A, as shown in Fig 4-26 or at any other location defined with basic dimensions relative to the datum feature simulator as in Fig 4-28."

Based on the attached drawing and not knowing anything else about the assembly of this part, I might assume the 2 diameters marked B, would be used to establish the Y origin and the X axis. And, if interpret the above spec, I might assume that X origin is the midpoint between the 2 diameters. However, in the later part of the spec, where is references "other location", would it be possible to interpret the diameter on the right as being the X origin?

The plot thickens. On the mating part, they use a pin on the right and a diamond pin on the left. Knowing this, might sway me to believe the diameter on the right should be the X origin but we don't always have access to this info.
. Pattern of Features for Datum Dwg.pdf

Pattern Of Features for Datum.pdf

[[Me...]]

Based on the drawing I would interpret the X and Y origin as the symmetry point of the 2 holes with neither having precedence over the other.

[[An...]]

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[[Ke...]]

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Agreed

[[To...]]

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[[Me...]]

I don't see how you could justify it. The 2x, FCF referencing both, and the B datum identifier attached all denote a pattern. The basics are also supporting the symmetry of the holes as the Datum location. I suppose you could argue that the 20 and 40 dims come from the right hole, but you'd have to ignore the other things I stated.

If the intent is that the right hole is the datum then the drawing is technically incorrect.

Just to add: The basics could be any type of distance, angle, whatever, as they are theoretical perfect and only used to define the nominal. You could have (2) 20 dims from center, an angle to a point 3 inches off the part and back to another feature, etc. It doesn't have any effect on the interpretation of the callout.

[[An...]]

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See attached.

Contribution_05_06_2020_1.pdf

[[Aa...]]

Forgive me for being daft, but unless they are using a customized DRF (specifying which degrees of freedom are constrained by which datum features), I don't see how where you position the origin is of any consequence. (I suppose this might matter if you're going to compare results using the coordinates of the different features.)