wim and rhinorudi, thanks for both of your replies.
I’ve just had several goes at the examples at the link that you showed, but none worked. Either I’m being a bit thick, or is it that this isn’t implemented in the Mac version?
I feared my explanation may confuse. It wasn’t specifically for drawing a rectangle, as much as saving having to transfer the result from a calculator (even as simple as adding together the thickness of several materials) into Rhino, thus avoiding typos and the like.
I’ll have another look at the link, and see what I missed.
Cheers.
Chris