When
GD&T is used, the geometric tolerances apply to the
features - not the dimensions. Therefore when BASIC dimensions
are used with geometric tolerances, several different
dimensioning schemes may be used without changing the meaning
of the drawing. The first drawing below is an example of
baseline dimensioning. The other two illustrate chain
dimensioning. Since the position tolerance is related to
datums A, B and C, all three drawings have the same meaning
even though the dimensioning is different. This would not be
true if the dimensions locating the holes were toleranced
rather than BASIC. Because the meaning of these drawings is
the same, the designer should consider the needs of those who
will read the print when placing dimensions.
