106 Geometric Dimensioning and Tolerancing Datum Axis Established with Datum Target Symbols Datum target points, lines, or surface areas can also be used to establish a datum axis. A primary datum axis can be established by two sets of three equally spaced targets—a set near one end of the cylinder and the other set near the other end, as shown in Example 3-33. Notice the datum target points in the circular view are rotated as needed to align with an imaginary line projected from the center for clarity. Primary datum axis Example 3-33. Establishing a primary datum axis with target points.