One can calculate the angles if you first draw a line
for local noon
and use the following equation to calculate each hour line from that
noon line.
=20
X = hour lines angle ( each hour is 15 degrees )
Y = 90 - Latitude angle
Called the 'Colatitude' in some books.
Z = Angle on plate that is level to the ground from
noon line
arctan( tan(X) / cos ( Y ) ) = Z
At least I think I did the trig right.=20
I beleive that is correct, However, it gets more complicated if you want
to have a vertical-ish dial plate (say on a wall) that is neither truely
vertical (it 'reclines') and which doesn't face any of the cardinal
compass directions (it 'declines').
-tony