86 Geometric Dimensioning and Tolerancing feature. These points of contact, referred to as high points, take into account possible irregularity in the manufacture of the part within design limits. Positioning the part in the datum reference frame in this manner ensures a common basis for measurements. Degrees of Freedom All parts have six degrees of freedom. There are three translational degrees of freedom and three rotational degrees of freedom. The term degrees of freedom means the number of coordinates it takes to exclusively control the position of a part. The term translational refers to uniform movement without rotation, and the term rotational refers to movement around an axis. Considering the datum reference frame in Example 3-11, the part can move without rotation in each of the three directions from the mutually perpendicular planes. This is called the three degrees of translation. The part can also rotate about each of the axes, which is referred to as the three degrees of rotation. Refer again to Example 3-11 and notice that the three translational degrees of freedom are labeled x, x , x y, and y , and y z. The three rotational degrees of freedom are labeled u, v, and v , and v w. The following demonstrates the degrees of freedom related to the primary, secondary, and tertiary datums: The primary datum plane constrains three degrees of freedom: • One translational in z. • One rotational in u. • One rotational in v. Datum axis Secondary datum Tertiary datum Primary datum Datum axis Part Datum axis Three Mutually Perpendicular Planes Example 3-11. All parts have six degrees of freedom. The three translational degrees of freedom for this part are labeled x, y, and z. The three rotational degrees of freedom for this part are labeled u, v, and w.