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Geoffrey,
What are some example of a Vernier sextant, please? 
If a description was posted earlier, I missed it.
Thank you,
Steve

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Geoffrey Kolbe
Sent: Monday, October 19, 2015 12:52 PM
To: steveebryant@att.net
Subject: [NavList] Re: Degrees and minutes vs decimal degrees and theDaily Pages

On Mon, Oct 19, 2015 at 3:37 PM, Brad Morris  wrote:

> ​As an​
>  interesting side note, you never have to remember to approach contact in
> the same direction with a vernier.  The tangent screw does not provide the
> reading, and as such, gear lash is irrelevant.  With a micrometer drum, you
> do.
>
> ​Quite so​


In principle, there is no doubt that vernier will be more accurate than
drum. A vernier is a direct reading of the position of the index arm
against the arc.

A micrometer drum sextant is easier to read, but the assumption is that the
thread on the tangent screw is uniform and free of errors (on both sides of
the thread), that it is free of backlash, that the index arm is free of
flexure, or side movement​ - which depends on the tapered journal bearing
on the index arm be perfectly tight, etc. That requires a much higher level
of technical excellence than is required in a vernier sextant.

Geoffrey Kolbe


: 

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