IV 10 Help
Tools - Document settings - Units
Sets the default units system and dimension precision for the active model file or template.
Note: To change the default units system applied when you create new files, change the default units in the templates that you use to create files.
When you installed Autodesk Inventor, you specified a units system that is automatically assigned to all new files. You can change the automatically assigned units by editing the templates used to create new files, or replacing the templates with your own.
Note: Templates are in the Autodesk\Inventor<version>\Templates folder. Any part, assembly, or drawing file becomes a template if you save it in the Templates folder or any of its subfolders.
Hope this helps.