# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: MkIXa bubble sextant performance
From: Jean-Philippe Planas
Date: 2007 Apr 4, 22:41 -0700
Hi Alex,

Did you try to identify an Index error or any systematic error?
Did you solve the issue of the bubble getting bigger during the observation after having been reduced when starting the observation session?

alex <eremenko@MATH.PURDUE.EDU> wrote:

After a month of practice, I can find my position within 2-3 miles
with this sextant.
The use of the averager gives better results than a single
observation.
But averaging 5 single observations by hand gives the same precision
as the mechanical averager does (it averages 60 observations).

Here is a typical complete fix with the averager:
GMT April 3, 1:28:46 Sirius 28d22' ; 1:51:55 Venus 15d18'.5
Using DR 40N, 87W, I obtain
Alt of Sirius 28d44'.2, Azimuth 207d,
Alt of Venus 15d12'.8, Azymuth 282d.
Correcting for refraction and plotting on the Universal Plotting Sheet
gives this position 40d20'.5N, 86d54d.5W, as read from the
plot with 0'.5 resolution.
My true position was 40d27'.2N, 86d55.8W,
so the error is slightly more than 1 mile.

In this reduction I used the Complete on Board Celestial Navigator,
which is not very precise but very handy indeed.

Here are two typical series of individual observations (averager off,
reduced
with the Almanac and computer).
Venus, errors: 1'.8, -2'.4, -0'.9, -0'.2.
Sirius, errors: 1'.2, 1'.7, 3'.0, 0'.0, 1'.8.

Alex.

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