RE: Drawing hour lines

[Cordasco, Anthony (NJ Data Services)]

Question:
If hour lines do not lie on the same plane as the base of the gnomon must
they shift and if so does anyone have a formula for this. 
Lets imagine concentric circles with 4", 6", 8" and 10" concentric circles
each rising 1/4" above each previous one. If the hour lines are cut into the
surface of each circle, how would one compute the shift in hour lines? Would
it be a significant enough shift or would straight hour lines suffice?
Thanks,
Anthony