5.9.1 Rectangular Coordinate Method. For holes located by rectangular coordinate dimensions, separate feature control frames are used to indicate the direction and magnitude of each positional tolerance relative to specified datums. See Fig. 5-41. The feature control frames are attached to dimension lines applied in perpendicular directions. Each tolerance value represents a distance between two parallel planes equally disposed about the true position.
5.9.2 Polar Coordinate Method. Bidirectional positional tolerancing is also applied to holes, such as gear-mounting centers located by polar coordinate dimensions relative to specified datums, where a smaller tolerance is desired in the direction of the line-of-centers rather than at right angles to the line-of-centers. See Fig. 5-42. In this application, one dimension line is applied in a radial direction and the other at right angles to the line-of-centers. A further requirement of perpendicularity within the positional tolerance zone has been specified. The positional tolerance values represent distances between two concentric arc boundaries and two parallel planes, respectively, equally disposed about the true position. Coordinate hole-locating dimensions, indicated as reference, may be included on the drawing for manufacturing convenience.
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