Hi Fer, > The ring dial you noted is in fact an equatorial sundial. > In use its inner ring lies in the equatorial plane. > The inner diameter of that ring is R. > The point on the date scale is from the centre: y = R tan decl. > Decl is the declination of the sun, relative to the date. > It is the angle the sun is north or south the equator.
This is great! It was what I was looking for :) Thx very much, weemeng -
