NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A basic sight reduction question
From: Stan K
Date: 2012 Apr 4, 13:25 -0400
From: Stan K
Date: 2012 Apr 4, 13:25 -0400
Gary,
Yes, it seems like nobody ever noticed that situation!
I understand all this, but it doesn't help. The problem is not with the mathematics but with the proper procedure when doing an "on paper" sight reduction, i.e. with a typical sight reduction form. It still seems that if you follow the instructions in the Almanac, for the 0 minutes case we are discussing, any time the v or d value is between 6.0' and 17.9', for example, you would be adding a v or d correction of 0.1' to the hour value on the daily page, which appears incorrect.
And when would the v and d data of the 0 minutes column ever be used? When there are 0 minutes but non-zero seconds? Not according to the Almanac instructions.
I've looked for an e-mail address for someone at the UK Hydrographic Office. Know of any?
Stan
Yes, it seems like nobody ever noticed that situation!
I understand all this, but it doesn't help. The problem is not with the mathematics but with the proper procedure when doing an "on paper" sight reduction, i.e. with a typical sight reduction form. It still seems that if you follow the instructions in the Almanac, for the 0 minutes case we are discussing, any time the v or d value is between 6.0' and 17.9', for example, you would be adding a v or d correction of 0.1' to the hour value on the daily page, which appears incorrect.
And when would the v and d data of the 0 minutes column ever be used? When there are 0 minutes but non-zero seconds? Not according to the Almanac instructions.
I've looked for an e-mail address for someone at the UK Hydrographic Office. Know of any?
Stan
-----Original Message-----
From: Gary LaPook <garylapook@pacbell.net>
To: NavList <NavList@fer3.com>
Sent: Wed, Apr 4, 2012 12:46 pm
Subject: [NavList] Re: A basic sight reduction question
From: Gary LaPook <garylapook@pacbell.net>
To: NavList <NavList@fer3.com>
Sent: Wed, Apr 4, 2012 12:46 pm
Subject: [NavList] Re: A basic sight reduction question
I never noticed the situation that you pointed out. The answer is that the "v" and "d" correction tables in the N.A. are simply multiplication tables, multiplying the "v" and "d" factors (which are simply how much the body changes its position in one hour) by the proportion it will change in a period less than a full hour. Since the tables only list correction for whole minutes they are actually the average correction for the whole minute tabulation so they are actually calculated for m + 30 seconds. They can be considered precise only for the +30 sec case and approximate for other times. If you wanted more precision then just divide the "v" or "d" by 3600 and multiply by the number of seconds after "on the hour." If you do it this way then you will find the correction for "on the hour" is zero, zero seconds times any "v" or "d" value will always equal
zero. But you are trying to make it too hard on yourself. gl --- On Wed, 4/4/12, slk1000@aol.com <slk1000@aol.com> wrote:
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