Art, You are, of course, correct. And if the FAQ committee prefers to go with your approach, I have no objection.
The picture I had in mind was slowly turning the dial around to simulate various hours of the day. Since looking at shadows cast on the dial by the gnomon is the modus operandi for the dial, I thought it would be a good test procedure. Art Carlson wrote: > Jim_Cobb <[EMAIL PROTECTED]> writes: > > > I've thought of another tip for spotting worthless horizontal sundials > > (such as is sold in garden shops, etc)--if the shadow of the gnomon > > crosses the hour lines it's no good. This test requires only > > horizontal positioning, not polar alignment, and a lot will fail this > > test because the gnomon for cheap dials often does not intersect the > > dial plate at the convergence point for the hour lines. > > Actually it doesn't require horizontal positioning either, or even a > shadow. For each hour line, you should be able to find a position for > your eye such that the edge of the gnomon is superimposed on the hour > line. If they ever "cross", i.e., if you can ever see part of the hour > line above the gnomon but not all of it, then the gnomon will not > intersect that line in the dial plate, and the dial is "worthless". > > --Art Carlson
