About Declaring Datums
To facilitate automatic assembly, global datums created in a notebook are declared in each part of the assembly. Before you can declare datums, you must declare the assembly and parts to the appropriate notebook.
Datum plane orientation is shown by an arrow. Choose Flip from the Direction menu to change the datum plane orientation (or all the members of a pattern of datum planes).
The following rules apply when declaring datum planes:
Axes and datum planes can be declared in Part mode only.
If you have used a reference axis or datum plane in a declaration, you cannot delete it from a notebook unless you delete the corresponding part entities and undeclare the notebook.
When you explicitly declare a datum, you select the part or assembly datum and enter the name of its global reference. The datum then appears with a global name. Explicit declarations are simple to use and easy to visualize but have two limitations. You cannot:
Have two datums on the same model with the same explicit declaration (two datums with the same name).
Have one datum with two different explicit declarations (one datum with two names).
Use a table declaration to declare more than one datum in a component to create a placement definition (for example, to assemble a bolt automatically into many holes in a plate).