The Dimensioning and Tolerancing Standard (ASME Y14.5M – 1994) puts forth fourteen fundamental rules and two general rules. The fundamental rules control the clarity and intent of dimensions and tolerances. These rules are usually covered, in one form or another, in conventional engineering graphics text book. The general rules affect the application of GD&T and are assumed to be true unless otherwise specified on the engineering drawing. At this point, the following general rules do not have any foundation/background for understanding. However, they are stated here as reference. The following are the general rules as stated in the ASME standard.
Rule#1: Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its form, as well as in its size, are allowed.
Rule#2: Regardless of feature size (RFS) applies, with respect to the individual tolerance, datum reference, or both, where no modifying symbol is specified.