To Create Custom Units
You create a custom measurement unit in the same way you create a custom system of units, by using the Units Manager dialog box.
1. Click File > Prepare > Model Properties. The Model Properties dialog box opens.
2. Click change in the Units line. The Units Manager dialog box opens to the Systems of Units tab.
3. Click the Units tab. All system-defined and custom units are listed. A description of the selected unit appears under Description.
4. Click the New button. The Unit Definition dialog box opens.
5. Select a physical dimension from the drop-down list provided.
6. Under Unit Definition, do the following:
Under Name, type a name for the new unit or accept the default name.
Enter a scale, and then select a reference unit from the drop-down list. The default unit is in (inches).
7. Click OK to close the Unit Definition dialog box, and then click Close to close the Units Manager dialog box.
* 
Use the Copy button to create a copy of the selected unit with a different name. You can also rename a unit by using this procedure.
You cannot edit or delete system-provided units. System-provided units are indicated by the PTC icon under Description.