System vs. Display Units
It is important to note the distinction between System and Display units. Display units only affect how geometry is displayed in the viewports. System units determine the actual scale of geometry. For example, if you import a DXF file (unitless) containing a 1 x 1 x 1 Box, 3ds Max may import the box’s dimensions in inches or miles, depending on the System unit. This can have a significant impact on your scene, which is why you should always set up the system unit before you import or create geometry.