Good question.

So it sounds like you have successfully found the Units properties amongst the Project properties by selecting the menu item File->Properties. In the Properties panel if you expand Units you can see all the units, e.g., Length, Force, Mass.

Taking Length as an example, the default name is 'm' for meters and if you expand Length you will see Scale, which is set to 1 by default. If you want to change Length to inches, then, as you said, you would change Length from 'm' to 'in' and the length Scale from '1' to '39.370' - that is the number of inches in 1 SI length unit (meter). The principle holds for the other units. So for the units you mentioned:

• Force lbf Scale = 0.2248 (i.e., 1N = 0.2248lbf)
• Mass lbm Scale = 2.2046 (i.e., 1kg = 2.2046lbs)

If you want to keep these custom units as defaults, then I suggest you save an empty project (.sym) with these setting and then use that 'template' project file as the basis for all your simulations.

By default all imported geometry is assumed to be in meters.

Hope this helps.