We have a pattern of holes which are located using ordinate dimensions. Their tolerance zones are specified using a position tolerance frame, so the dimensions themselves are basic.

What dimensions are basic?

In Geometric dimensioning and tolerancing, basic dimensions are defined as a numerical value used to describe the theoretically exact size, profile, orientation or location of a feature or datum target.

When should a dimension be basic?

Basic dimensions are used to establish the "true profile" which a profile tolerance will then control. So if a profile tolerance is applied to a hole, the diameter MUST be a basic dimension. There are two methods of dimensioning described in Y14. 5: rectangular coordinate dimensioning and geometric tolerancing.