Thanks Gaieus and b for your suggestions.

G, I'm not trying to snap to section cuts as I realise these are not snappable points, I think it's snapping to the floor/wall intersections.

b: model layer is not locked; dim layer not shared; yes, I'm getting inference and snap to my model (and for that matter, it works just fine). I know I'm not in model space because a/ no blue circles, and b/ if I option drag the dimension to a non-perpendicular angle with respect to the measured segment then the length of the dimension changes.

I have opened the other forum member's drawing again and can get the blue circles on his model but I can't get them on mine...

Running OX10.6.5 w/ SU8.0.3161 LO3.0.3161

Dimensioning architectural plans in LO3 and can't get them to attach to model space consistently. I almost never get the round circles. In fact I saw them for the first time today when I imported a LO file from another forum member et voila - for a brief period I got them in my LO too! But I can't repeat it.

I use section planes and "align view" to create orthogonal views for every plan and elevation. Insert these to LO and then correct the scale to 1:100 (and hope it stays 1:100). These are placed on a layer called "viewports" (I used to lock this layer until I read that dims won't attach to a model on a locked layer). SU window always says "(modified) scene name" and ortho can't be unchecked nor can the standard view "top" be overridden.

I understand from reading this topic
http://sketchup.google.com/support/bin/answer.py?hl=en&answer=156796
that LO won't attach dims to model space in standard ortho scenes. Is the problem that LO thinks my custom scenes are standard?
BTW why would you have this default in your program if bjanzen says "dims in paper space are so 1990"?

Any help appreciated
Cheers
Norm