The tolerance values in the feature control frame are followed by up to three optional
datum reference letters and their modifying symbols.

A datum is a theoretically exact point, axis, or plane from which you make measurements
and verify dimensions. Usually, two or three mutually perpendicular planes perform
this task best. These are jointly called the datum reference frame.

The following illustration shows a datum reference frame verifying the dimensions
of the part.

Learning AutoCad

sp Feb 2016 … A datum reference frame is a coordinate system against which the geometric dimensions and tolerances of a part are defined. The main function of the datum reference frame is to specify a foundation for the inspection of the part. It is the common coordinate system of all tolerance zones.About Datum Reference Frames. The tolerance values in the feature control frame are followed by up to three optional datum reference letters and their modifying symbols. A datum is a theoretically exact point, axis, or plane from which you make measurements and verify dimensions.Datum reference frames are used as part of the feature control frame to show where the measurement is taken from. A typical datum reference frame is …Datum Reference Frame. Recently a client asked me to look at a drawing that is similar to the one shown in Fig. 14-14A below. The primary datum  …… The datum reference frame is not absolutely perfect, but it is made sufficiently accurate with respect to the part to consider it to be perfect.frame that uses this datum feature as a reference. A feature control frame can reference multiple datums at …… What's a datum reference frame? As discussed in workshop No. 5, datum reference frames (DRF) are coordinate systems, and preferably—at …… In our last workshop we investigated the anatomy of Feature Control Frames including their structure, the purpose of their various …29 Jan 2010