Other Modules > Working with Geometric Tolerances > To Set a Reference Datum
  
To Set a Reference Datum
1. Click Insert > Geometric Tolerance.
2. Click Set Datum on the GEOM TOL menu.
3. Select the datum plane or axis to be set. The datum is enclosed in a feature control frame.
To place a set datum in a note or dimension, edit its text and type: @[-D-.
This produces the following: