Thanks for the advice.
1) I will add my software title to my signature - I did say in my post I am using Home Designer Pro 10 because I knew it would be needed.
2) I have already set the snap to dimension to 1 mm, so I assumed I should be able to snap to that smallest dimension but that doesn't seem to be the case.
3) Sorry, I didn't use the built in help because in most programs it is usually not good, but I see in HDP it seems to be useful. My search of Google didn't produce any good results so I came here. I'll do more reading in the built in help.
Thanks for the quick reply and pointers.