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The tolerance in the
upper segment of a composite tolerance is located by all
applicable basic dimensions. On the drawing above, the red
tolerance is located by the red dimensions.
The lower segment of a
composite tolerance does not use the basic dimensions which
originate at the datums. Only the basic dimensions within the
pattern are applicable. If a datum is repeated, it indicates
that the orientation of the pattern must be held to the
tighter tolerance. In this case, the perpendicularity to datum
A must be within 0.2 and the pattern of two holes may not tilt
more than 0.2 relative to datum B.
You
will now notice that there are two position symbols being
used. This callout is not composite. It is called two single
segments. The upper segment has the same meaning as the upper
segment of the composite callout shown earlier. The lower
segment, however, improves the location as well as the
orientationof the feature(s) relative to the datums referenced
in the second sement. Notice that the 19mm dimension from
datum B is shown in red. The pattern must be positioned at the
19mm dimension from B within 0.2 total even though the pattern
may be out of position as much as 0.6 total relative to datum
C.
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