Transcription: Multiple datums may be used on a single object. In this three-plane datum system, the planes are at right angles to each other. The order of the planes is important since the object contacts the first plane at three points, the second at two, and the third at only one point. This procedure is done to prevent any rocking due to part distortion, which could possibly alter the measurements. Datum surfaces are not required to be perpendicular to each other.
(.mp3)