NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A new way to apply sextant corrections
From: Jeremy C
Date: 2011 Feb 1, 09:14 -0500
From: Jeremy C
Date: 2011 Feb 1, 09:14 -0500
I tried it, but it doesn't really work for my personal methodology. I
prefer to calculate a standard sight in three parts: Hs-Ho, Time to LHA, and
then Dec to intercept and azimuth. Column subtraction doesn't bother me,
so your method is more cumbersome for me to use than mine. Of course
YMMV.
Jeremy
In a message dated 2/1/2011 11:36:59 A.M. Central Asia Standard Time,
glapook@pacbell.net writes:
I posted this sextant correction form about a week ago and there have been no comments about it, has anybody given it a try?
gl
--- On Mon, 1/24/11, Gary LaPook <glapook@pacbell.net> wrote:
From: Gary LaPook <glapook@pacbell.net>
Subject: [NavList] A new way to apply sextant corrections
To: "Navlist" <Navlist@fer3.com>
Date: Monday, January 24, 2011, 6:14 PM
I have found it difficult to subtract a series of numbers in a column, it is much easier (and less prone to error) to add a series of numbers. When using the Nautical Almanac, the normal way to correct the sextant altitude (Hs) to obtain observed altitude (Ho) involves both adding and subtracting various correction factors. The index correction (IC) can be either added or subtracted and the same for semidiameter (S.D.) and temperature and pressure (T&P). Dip, refraction, and the 30 minute additional factor for upper limb of the moon are always subtracted and parallax is always added. Normal procedure for flight navigation is to pre-compute the sights and reverse the signs of these corrections and apply them to Hc (computed altitude) to obtain Hp (precomputed altitude) so that no time is lost in figuring the intercept. If you give it some thought you will see that applying sextant corrections, with reversed signs, to Hc will result in the same intercept as when making the corrections in the conventional manner.
Using this equivalence, I decided to make a correction form that involves only addition, no subtraction. If the sign of the correction is plus I add it to Hs. If the sign is minus I add it to Hc. I have attached a PDF file with this form. At the bottom you copy the smaller of Ho or Hc beneath the opposite column and then subtract to find intercept.
Give it a try.
gl
