To create a GD&T Datum item

Use GD&T Datum items to identify specific features for use as datums in GD&T items, and to assign names to those datums. Using GD&T Datum items has two advantages:

• You can specify the feature symbol for the datum so you can use the same symbol for a GD&T Datum as that used in the CAD.
• You can specify and change the datum items used in several GD&T measurements by changing the reference feature used in the GDT Datum item.

To create a GD&T Datum:

1. Open a Geometric group in the inspection sequence.
2. Click Geometry tab > GD&T panel > Datum. The GD&T Datum dialog is displayed.
3. If you want to exclude this item from the report, deselect the Output in report check box.
4. In the Datum feature symbol box, type the name you want to use for the datum when it is displayed in a control frame. You can specify one or more capital letters except I, O, or Q.
5. By default, the name by which a GDT Datum item is referred to in the inspection sequence and in other items is based on the Datum feature symbol. To specify a different name for this item, click and edit the Name box.
6. In the Reference feature list, select the item you want to use as the datum.

   Ensure the reference feature lies within the angular tolerance of all the items that reference it.

7. Click OK to create the GD&T Datum item and close the dialog. The item is available for selection in the Datum lists of GD&T measurement items. For example:

   

You can identify when a GDT Datum item is used in a GD&T item by the background of the reference symbol in control frame: for GDT Datum items, the reference symbol is shown against a white background; for sequence items, the reference symbol is shown against a patterned background.