92 Geometric Dimensioning and Tolerancing Datum Target Points Datum planes are established by the datum target points as follows: The primary datum plane must be established by at least three points on the primary datum surface. These points are used to provide stability on the primary plane, similar to a three-legged stool. The secondary datum plane must be located by at least two points on the related secondary datum surface. Two points provide the required stability for the secondary plane. The tertiary datum plane must be located by at least one point on the related tertiary datum surface. One point of contact at the tertiary datum plane is all that is required to complete the datum reference frame and provides complete stability of the part in the datum reference frame. Baseline or chain dimensioning can be used to locate datum target points. The location dimensions must originate from datums. Datum target points are established on the drawing using basic or tolerance dimensions. Established tooling or gauging tolerances apply when datum targets are located with basic dimensions. Datum targets are established on the part with fixtures and with pins. These pins contact the part where the datum targets are specified. Example 3-16 shows a pictorial drawing of the datum target points on the primary, secondary, and tertiary datums. Three points of contact on primary datum One point of contact on tertiary datum Two points of contact on secondary datum Example 3-16. Datum target points on primary, secondary, and tertiary datums.