If a profile tolerance is independent, what is its relationship to datums?

If a profile tolerance is independent, what is its relationship to datums?

• A. It is defined relative to the primary datum
• B. It is defined relative to all datums equally
• C. It is not referenced to any datums; the relation is defined by the FCF.
• D. It requires a datum target

Answer: (C)

Profile tolerance that is independent means the tolerance zone for the surface is set without tying it to any datums. In other words, the way the surface is allowed to vary is not defined relative to a datum reference frame by default. If you want datums to influence how the profile is checked, you specify that relationship explicitly in the feature control frame by including datum references there. Otherwise, there is no inherent datum relationship—the relation to datums is defined by what you place in the FCF. So, the independence implies no automatic reference to any datum; the datum relationship, if needed, is provided in the FCF itself.

Profile tolerance that is independent means the tolerance zone for the surface is set without tying it to any datums. In other words, the way the surface is allowed to vary is not defined relative to a datum reference frame by default. If you want datums to influence how the profile is checked, you specify that relationship explicitly in the feature control frame by including datum references there. Otherwise, there is no inherent datum relationship—the relation to datums is defined by what you place in the FCF.

So, the independence implies no automatic reference to any datum; the datum relationship, if needed, is provided in the FCF itself.