John couldn't work out an Email address or I'd have replied direct! My slate dial was a simple affair, about 6inches square with a brass gnomon of ordinary angular design. I engraved roman numerals, with what I can't remember, but my slate was fairly soft and it was quite easy. From what I have seen some types of roof slate would be a lot harder and probably thinner (My bit was about 0.75 inches thick.)
A vertical dial would be fun to make with your piece of stone. I think if I were making a vertical slate I might use iron for a gnoman, try to give it a old feel. Don't know what your math is like but the mark-out angles would be calculated from:- Hour Line = ARCTAN ( TAN (H) * COS (L) ) Where L is your latitude and for H 12 noon H=0 11/1 H=15 10/2 H=30 9/3 H=45 8/4 H=60 7/5 H=75 6/6 H=90 All this assumes a vertical dial facing due south, or thereabouts, depending how fussy you are :-) The gnomon would angle 90 minus latitude from the wall. If the wall isn't due south then the sums get harder, and the gromon, which always points to the pole-star has to be skewed. Go ahead make it! Sorry if all this is obvious, I havn't had chance to get the tone of the list! Alan
