Alistair, I always use decimal degrees, I find it a lot easier and more natural for my simple brain. Note that I have been using 0.25d on my original azimuth scale with a fixed magnifying glass and I have absolutely no trouble finding my targets. My only problem is recognizing a faint object.
Using the vernier as I have drawn it your are able to read 0.1d much easier even without magnification.
Have you looked at the link on Bojan's post
http://en.wikipedia.org/wiki/Vernier_scale very informative.
Anyway, let us know if you need to change anything, I am more than happy to draw up to your needs. It's up to you to tell me the actual size/radius and which side you need the vernier.
Cheers
Richard
ps Just saw that you added a new post before I posted this one, I'm very slow at this
Sent you a PM