Chapter 1 Geometric Dimensioning and Tolerancing Essentials 19 Copyright Goodheart-Willcox Co., Inc. Example 1-15 shows using a parallelism geometric tolerance to achieve a parallel surface design requirement for the face plate. The parallelism tolerance specification provides a more complete definition of the part requirements. Parallelism, explained in Chapter 7, is the condition of a surface or center plane equidistant from a datum plane. Parallelism is also the condition of an axis equidistant along its length from a datum plane or a datum axis. A parallelism tolerance establishes a tolerance zone defined by two parallel planes, two parallel lines, or a cylindrical zone parallel to (at a Orthographic View Meaning 16±0.5 between the vertical surfaces 16 – 0.5 = 15.5 16 + 0.5 = 16.5 0.5 + 0.5 = 1 tolerance Goodheart-Willcox Publisher Example 1-14. In coordinate tolerancing, the features of a part are defined with directly toleranced coordinate dimensions. The tolerance applied to the linear dimension specifies the maximum and minimum limits. Notice the allowable surface variation of the part. The part could also be bent out of form.