fig. 2-5 relating dimensional limits to an origin two parallel surfaces of unequal length is to be mounted on the shorter surface. In this example, the dimension origin symbol described in para. 3.3.16 signifies that the dimension originates from the plane established by the shorter surface and dimensional limits apply to the other surface. Without such indication, the longer surface could have been selected as the origin, thus permitting a greater angular variation between surfaces.
2.6.1 Dimensional Limits Related to an Origin. In certain cases, it is necessary to indicate that a dimension between two features shall originate from one of these features and not the other. The high points of the surface indicated as the origin define a plane for measurement. The dimensions related to the origin are taken from the plane or axis and define a zone within which the other features must lie. This concept does not establish a datum reference frame as described in Section 4. Such a case is illustrated in Fig. 2-5, where a part having
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