Understanding constrained contact measurements

[[Ja...]]

Hi,

I have a question about a common blueprint note: "all dimensions apply when -B- maintains a clearance envelope of ØX and surface -A- is flat within Y in free or constrained state. constraint contact allowed on A,B,C surface"
Let's say the part is cylinder or ring. surface A and C are opposite faces of cylinder and B is the ID of cylinder.
To apply these constraints, a fixture is made with OD of ØX. The part is placed inside the fixture with datum -A- facing down and clamps on datum -C- face.

Now the question:
1) If the print calls for diameter -B- to be measured, does it still have to constrained? ( if yes,I would need to have fixture height little less than height of diameter -B- to actually probe diameter -B-, and doing so will it not violate the note requirement? )
Or, diameter -B- is to be measured in its free state?
dimension -B- as noted in B/P: Ø M ± n AVG
[O| .010 free state]