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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Degrees and minutes vs decimal degrees andtheDaily Pages
From: Stan K
Date: 2015 Oct 18, 16:44 -0400
From: Stan K
Date: 2015 Oct 18, 16:44 -0400
David,
The smiley at the end of the sentence was meant to imply an exaggeration. No, vernier sextants, as opposed to micrometer drum sextants, are not impossible to use, just orders of magnitude more difficult (IMHO). The scales are small and low contrast and need magnification. And there are several times as many marks to look at to see which one lines up the best. Reading them is a two-step operation. In your photo, step one is to recognize that the reading is over 67º30'; the second step is to use the vernier to determine the value between 30' and 60'. If you say it appears to be reading 67º47', then the 17' mark on the vernier must be the one that lines up the best. Too tough for my eyes!
I have a beautiful old Hezzanith vernier sextant which gives me a headache to use. Yes, as you said, you have to stare at the reading for a long time to make sense of it. Give the guy who invented the micrometer drum sextant a pat on the back!
Nevertheless, you also get a pat on the back for what is in the photo.
Stan
-----Original Message-----
From: David Pike <NoReply_DavidPike@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Oct 18, 2015 4:12 pm
Subject: [NavList] Re: Degrees and minutes vs decimal degrees andtheDaily Pages
Attached File:
(f1-Ply-Sextant-Scale-Close-Up-Large.JPG: Open and save)
From: David Pike <NoReply_DavidPike@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Sun, Oct 18, 2015 4:12 pm
Subject: [NavList] Re: Degrees and minutes vs decimal degrees andtheDaily Pages
Stan you said "vernier sextants are impossible to use anyway ;-)"
I'm not sure what you meant by that. Did you mean sextants with the vernier against the arc, or sextants with a vernier against the drum? Did you mean the vernier itself was impossible to use, or were you referring to the fact that they're probably quite old and have smaller mirrors than todays sextants and the marks on the arc are getting worn? Perhaps you just meant you have to stare at the reading for a long time to make sense of it. I suppose that's why the old sextants had a swing-over magnifying glass. My attempt below would have been OK if I'd just had a bit more patience shaping the edge, but I was running out of time. I can't even remember now if I was supposed to make it one division too large or too small or if it mattered. I don't think I used the dividing engine as I did on the arc (you might say "That's pretty obvious"). It appears to be reading 67° 47'. DaveP
Attached File:
(f1-Ply-Sextant-Scale-Close-Up-Large.JPG: Open and save)
