A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2016 Feb 18, 12:23 -0800
Thank you for the three photos Ed. They’re much more expandable. They all seem to be of the front. Is it possible to have one of the instructions on the back? The more I look at the device, the more I think it’s for an astro compass or similar, which tilts allowing you to enter with LHA and declination rather than Hc and Az. With declination only accurate to ¼ degree and no epoch marked, you’re clearly not expected to work to any greater accuracy. On the other hand, if you were using it with AP3270Vol 1/HO249 and a sextant, you'd only need LHA Aries and lattitude; the rest is done for you. Q appears in the correct ball park bearing in mind no date is attached.
As far as I see from the snaps if LHA Aries was 344 at on a particular day, the calculator would give you the LHAs of Aries and the main navigational stars and their approximate declinations for any time until the day after, LHA Aries at increasing by approximately one degree per day. That’s why 24hrs doesn’t quite line up with 00hrs.
I’m still not clear about the longitude scale, which appears to be on the same disc as the time scale. There’s probably some clever way of calculating LHA aries from GHA Aries, or allowing for change of longitude during flight, but if you’re clever enough to work out how to do that, you’re more than clever enough to simply subtract longitude west or add longitude east. DaveP