I learned from a book (in teory) how to make an altitude ring sundial. 'Tis different from the equatorial ring, as it is devised specially for one certain latitude. My problem is that I can't manually lay out the hour/declination lines (to be transfered to the inner face of the ring) with the precision I want, my protractor has only 1 degree divisions, furthermore it is too much laborious to find the lines with pencil, eraser, protractor and compass. That's why I love equations and softwares, but it is very hard to find them for the altitude ring.
Methinks it is somewhat like the shepherd's dial, except for 'tis an horizontal cylinder rather than a vertical one. Can I use the diagram of the shepherd's dial? But then, what would be the "length of gnomon"? How can I calculate the diagram? I mean, it seems for me that the diagram is essentially the same despite the latitude, that its dimensions depend only from the ring's radius and width, and that the specification of the latitude is determined by the orifice in the ring in relation to the diagram and the point of suspension. Here's a picture of a ring nearly identical to that I wanna make (mine hasn't a movable circle with the hole, it's constituted of but one ring): http://tiny.cc/h9tty Here is a link to a sketch I made that I hope will make clear my problem: tiny.cc/9dtgi Please be indulgent with my poor English. Thanks for your time! Marcelo Manilio
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