By default, profile tolerance specifies a uniform tolerance zone equally distributed about the true profile defined by the basic dimensions. All elements of the surface must lie within the tolerance zone. An arrow from the feature control frame must point to the surface or extension line.

Position tolerance locates features of size. It defines a tolerance zone within which the feature axis or center plane must lie. The size of this zone determines the amount of variation allowed from true (theoretically exact) position. Basic dimensions establish the true position from the specified datums as well as the interrelationship between the features. See the next page for an pictorial view of the tolerance zones.

If there is no material condition modifier following the feature tolerance, the geometric tolerance applies regardless of feature size (RFS). When RFS applies, the specified geometric tolerance is independent of the actual size of the feature. The allowable geometric tolerance is limited to the specified value in the feature control frame (regardless).

The feature control frame below states that the holes must be positioned within a 0.6 diameter tolerance zone. Since there is no material condition modifier following the feature tolerance, it is implied to apply RFS. This requires the axis of each hole to be positioned within a 0.6 diameter position zone despite the feature’s size. There is no additional position tolerance allowed as the holes get bigger or smaller.

Profile of a line specifies a series of 2D cross-sectional tolerance zones along the true profile, within which each 2D surface element must lie. The cross-sections are not compared to each other as a single entity. When used with datum references and as a refinement of profile of a surface (see example below), it may be necessary to clarify the cross-sections are only oriented to the referenced DRF.