Alistair, if you can wait till tonight I'll draw up a set with the vernier. Drawing them up is no trouble, but fitting the vernier to your pivot will be slightly more involved than just fitting a pointer. But as Bojan pointed out it will be easier to read and more accurate
By the way, You might remember that I use one of those electronic inclonometers (Wixey) for my altitude, simpler still.
Cheers
Richard