The Units option lets you view the conversion factor (scaling value) the plug-in uses as well as modify the conversion units.
Activate the Automatic option if you want the 3ds Max FBX Plug-in to automatically identify, set, and convert units of the incoming file to match units of the host application.
When you activate the Automatic option, the Scene Units converted to option is disabled, although it shows the resolved unit & Scale Factor. If you disable the Automatic option, the Scene Units converted to option becomes available.
If you activate the Automatic option and the File Units match the system units, there is no need for scale conversion and the plug-in applies no conversion. The displayed Scale Factor is 1.0 in this case.
If you disable the Automatic option, you can select your own units with which to convert the file using the Scene units converted to menu.
For information about incorrect or unwanted scaling issues, see Why is my scene scaled differently in 3ds Max?
