Surfaces Coplanar with Profile.
It is often necessary to have two
or more surfaces act as though they were one. That means that
you want the surfaces to be located relative to one another
regardless of referenced datums. There is only one geometric
tolerance that locates surfaces-profile of a surface. The
drawing illustrates two ways to control the location and
orientation (parallelism) of two nominally coplanar surfaces.
If the parallelism approach is used, the surfaces might be
parallel to the datum plane but would not be controlled for
coplanar to each other.
composite profile of a surface, coplanarity is
controlled as well as parallelism. Therefore, the
surfaces may float up and down within the 0.4mm
tolerance zone which is centered on the 25mm BASIC
location but they must float together while remaining
parallel to the datum plane within 0.1mm.