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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Vernier explanation
From: Peter Monta
Date: 2022 Jun 26, 15:34 +0000
From: Peter Monta
Date: 2022 Jun 26, 15:34 +0000
Hi Juergen,
... and at least from the second photo there is no shifting in the 10 sec tick marks.So my feeling is: this is not the original or at least functioning vernier scale for this sextant, although it is beautifully engraved.
This might be due to the camera and parallax. The camera is nearly directly over the left part of the vernier frame, while it sees the right part of the vernier a bit from the side. Since the vernier is elevated a fraction of a millimeter over the arc, perspective would throw the vernier ticks progressively to the right a little.
You are right, though, the picture does give the appearance of no shifting; I admit I didn't look at it that closely. But it seems implausible that a new vernier was fitted to the sextant, from a donor sextant with exactly 60/59 the radius as this one, and with identical engraving style of the numerals like 0, 1, and 6.
The 20 units on the vernier scale should span only 19 degrees on the main scale.
Should span 19 degrees 50 minutes, though, right, if we don't count the three extra ticks to the left and right (which is a good feature)?
Cheers,
Peter
