For structural engineering problems, when I multiply a force (N) by a distance I generally want the answer in (Nmm) or (kNm) or units of that form.  Yet Maple simplifies the result to Joules, which doesn't mean a whole lot to me when I'm trying to find stresses and strains in structural members.

My question is, how can I define my own set of units that I'm comfortable with instead of having to accept the default Maple units?  I'm not having a lot of success customising units with Maple.