108 Geometric Dimensioning and Tolerancing A secondary datum axis can be established by placing three equally spaced targets on the cylindrical surface. Refer to Example 3-36. Example 3-36. Establishing a secondary datum axis with datum target points. Movable Datum Target Symbols and Datum Target Points The movable datum target symbol can be used to indicate movement of the datum feature simulator. When datum targets establish a center point, axis, or center plane on a regardless of material boundary basis, the datum feature simulator moves normal to the true profile and the movable datum target symbol can be used for clarity. The term normal is used in ASME Y14.5 and in mechanical engineering applications to represent a feature that is perpendicular to a plane surface and radial to a curved surface. Movable datum targets are datum targets that are not fixed at their basic location, are free to translate, and can apply to a point, line, or area. In Example 3-37, datum C uses movable target symbols. The part is fixed against datum target points A1, A2, and A3 primary, datum target lines B1 and B2 secondary, and datum target points C1 and C2 tertiary. Because datums B and C are referenced in the feature control frame as RMB, the datum simulator makes contact with the part. If the actual part is manufactured to the small size tolerance, then datum target points C1 and C2 are movable in order to contact the feature part. In this case, the movable target points move along the basic 45° angle that is attached to the movable