Hi Marc,

re:
> Concerning the unit, I'm not sure I understand what the "unit options" button is.
> Why is there a second set of unit system ?

The one on the main dialog sets the unit system for the current open model.

The one on the "Unit options" dialog that says "Default unit system" sets the default that is used when you initially start up MoI (if no template file is being used).

Changing the "Default unit system" does not change the current model units, it only changes what is used on start up.

- Michael