Is this a 'legal' callout? We have 4 holes thru the face of a cylindrical part. You know the drill - I can't include the actual print. If need be, I can mock something up.
Datum A = OD, Datum B = Top plane of cylinder, Datum C = 1 of the 4 holes. Should there not be a material modifier here on the position tolerance itself?? Or is the effect the same b/c Datum C is one of the 4 holes?
I'll contact our customer...but they won't likely respond for a month or two...
I'm leaning towards it being an invalid callout. ASME Y14.5 talks about the principle of applying zero tolerance at MMC but I've never seen any examples like your screenshot. Contacting the customer is the best approach here rather than second guessing. I would also ask them to confirm the interpretation of datum C - is it a single hole or is it all four holes as a pattern?
I'm going to agree with Neil here, and ask the customer if those bolt circles are individual or all 4 as a pattern. This definitely needs clarification. I can't find the print my company had with a similar Position of 0 with a material modifier on the datum sadly to see what engineering said about it.
There should be a (M) on the positional tolerance, regardless if it is a single hole or a group of holes.
Theoretically, there could be a small possibility that the part could fall within specification depending on the datum C (M) and the rest of the datum structure (and planets are aligned, sun at it's zenith and so on).
To follow-up...my customer recognized the error of their ways and pulled a new tolerance from somewhere for the individual holes. I'm told a corrected print will be forwarded sometime in the next decade.
I'm glad you received clarification from the customer. Without having a material modifier on the tolerance zone, the size of the tolerance zone can never change. Therefore, if it is defined as a zone of zero size (with no possibility of changing), then there actually doesn't exist a tolerance zone and thus it can never be occupied.