20 Geometric Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. basic 0° angle to) a datum. The controlled surface or axis of the feature must lie within the tolerance zone. In Example 1-15, the parallelism tolerance is applied to control a sur- face. This application refines control of the surface and establishes another requirement in addition to the size tolerance applied to control the size limits. Both tolerance require- ments must be met. All points on the surface controlled by the parallelism tolerance must be within the parallelism tolerance zone. In addition, the surface must be within the specified size limits when the part is produced. Orthographic View Meaning Feature control frame Datum feature symbol Primary datum feature (datum feature A) 16±0.5 From datum A to the vertical surface Datum plane A Parallelism geometric characteristic symbol 0.5 Total parallelism tolerance Datum feature A reference 15.5 Minimum 16.5 Perfect form envelope at MMC 0.5 Wide parallelism tolerance zone Two parallel planes parallel to datum A Possible parallelism orientation of surface Goodheart-Willcox Publisher Example 1-15. Using a parallelism geometric tolerance to control the parallelism of a surface. Notice that the 0.5 tolerance specified in the feature control frame is a total tolerance.