To Modify a Datum Reference to a Geometric Tolerance
1. Select a geometric tolerance.
2. Right-click and click Properties on the shortcut menu. The Geometric Tolerances dialog box opens.
3. Click the Datum refs tab.
4. Do one of the following:
◦ Add a new datum reference by converting an existing simple datum reference into a compound reference feature. Add a secondary or tertiary datum reference clicking either Secondary or Tertiary. Select a datum reference from the Compound list. Specify a material condition, if needed.
◦ Replace a datum reference with another datum. Click Primary, Secondary, or Tertiary (whichever is appropriate) in the Datum references box; then select a different datum name from the Basic or Compound list. If the datum that you want to use is not on the list, click Select... to select it in the drawing.
◦ Remove a datum reference. Click Primary, Secondary, or Tertiary in the Datum references box (whichever is appropriate); then select None from the Basic or Compound list.
5. Click OK.