To Set a Reference Datum
1. Define the active annotation orientation before creating the first annotation in any session.
2. On the Model Tree or in the graphics window, right-click a datum plane or datum axis and click Properties. The Datum or Axis dialog box opens.
Under Type, is selected by default.
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You can also open Datum or Axis dialog box by clicking Properties on the shortcut menu that appears when you right-click a datum plane or a datum axis, respectively, on the Model Tree or in the graphics window.
3. If required, type a new name in the Name box of the Datum dialog box and click OK.
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You can change the name by choosing Name from the PART SETUP or ASSEM SETUP menu.
You can blank a reference datum plane only by placing it on a layer and then blanking the layer.
The On Surface and Define options in the Datum dialog box are used to create 3D datums in drawings.
To return the datum to its unset state, click .