Hello, I'm new to the list and don't know much but am interested. I tried looking in the archive for this list but was unable to connect. I hope I am not repeating a question which has been asked 1000 times, but I probably am. 8-)
I saw in a shop a perforated ring dial with circumferentially-sliding perforation. I liked the look of it but now can't remember much of the technical specifics; I should have bought it or sketched it. I got to thinking about it and I think that near noon, it should be hard to discern one time from another unless the ring is very large since the sun's altitude peaks and recedes gently and this dial seems to be an altitude sensor. Is this a well-known problem of this type of dial? Also, I tried to draw the dial and I think even with the sliding ring, the scale for the time, located on the inside of the ring, must be two dimensional and not linear as I believe I saw on the product for sale in the shop. Is this true? The second dimension would be for different seasons. In drawing the dial, I said that the position of the perforation for a season would be the average solar altitude for that season. By average, I mean splitting the difference between the solar altitude at 8 am (or 4 pm) and noon. Is this the right way to lay out one of these dials? What scheme does one use? Thanks very much, John B 37.72 N 122.07 W PS: I read Waugh's book and that's where I learned the designation, "perforated ring dial". Is that what this is generally called? PPS: I hope you can figure out what I am saying. I am so new to this that I don't know the correct terminology.
