John Carmichael listed the pros and cons of azimuthal dials and concluded that "it is NOT an appropriate design for me to build".
Of his "pro" arguments: > 1. It looks different, original and pretty (especially if you like the > Batman logo!) > 2. It can be made to tell Standard Time > 3. It requires a simple vertical gnomon > 4. It can be designed by Fer's Spin program > 5. It is horizontal (usually), and horizontals are very commercial > 6. It tells time from sunup to sundown I have always placed great weight on number 2. Perhaps because I'm a physicist, I hate to see a machine that is an order of magnitude less accurate than its inherent possibilities (+/-15 min EoT compared to +/-1 min (of time) solar radius). An EoT chart is an awkward remedy. I got onto azimuthal dials (before I knew what they were called) as a way to build sundials that accurately show clock time, but also saw great possibilities for "different, original and pretty" designs (pro argument 1), and I offered my Arizona dial as an example. Now look at John's "cons": > 1. It requires an absurdly tall gnomon at middle and lower latitudes which > would make the sundial look odd and would have severe shadow fuzziness > problems in the summer. > 2. To avoid using a tall gnomon, the shadow must be artificially extended by > visual guesstimation or by a string shadow extender, both of which would > make the dial less precise. Also, changing the date ring order complicates > calculations and makes the dial even harder to read. > 3. It is inherently hard to read even with just one hour time lines, > especially for the novice, without instructions. > 4. It is very difficult to make this dial precise with small time line > divisions.(For fun, try Spin using five minute time increments (step > hour=5/60=.0833, and you'll see what I mean) > 5. Small time increments make the dial even harder to read. > 6. There is severe time line compression on the inner date rings, making > engraving and reading difficult. > 6. If the geniuses on the Sundial List have a hard time understanding it, I > doubt my customers ever will! These revolve around the short shadows of vertical objects at some times and places and the difficulty of reading the wildly curving lines. I think it is still possible to have the best of both worlds (except pro 3), specifically by using a polar gnomon. (Some other contributors are already playing with designs with concentric dates rings and non-vertical gnomons.) This would immediately eliminate cons 1 and 2 (too tall gnomon). It would be much easier to read, understand, calculate, and manufacture (the remaining cons, except perhaps the first of the sixes) because the would look nearly like a conventional sundial. The hour lines would be nearly straight since they only have to accommodate the EoT, not the declination. You can tell at a glance about what time it is (as with an uncorrected dial), or you can look for the date ring and tell the time within a minute or two. The flexibility of choosing the shape and location of the date rings remains (pro 1), so an Arizona dial, for example, is still possible. (Words, words, words! Will one of you that has been posting azimuthal dial plate designs please plug in a polar gnomon for me?) Are you interested in such a compromise, John? Regards, Art
