The size of the intercept as calculated from an AP has no meaning as to the accuracy of the shot, merely a coincidence of the error and the azimuth to the AP. The important measure is the distance from the plotted LOP and your actual position.
First thing to try. From your description of having to turn the leveling screw back after swapping the level end for end indicates that there is an error in the level itself since it should be level in either orientation. So try this, only remove half the error when you turn the level end for end. The bubble should be off center by the same amount in either orientation.
Since you are using an AP instead of your known position, any error in the measured altitude will be magnified when you plot it if the azimuth from your actual position to the AP is not at a right angle to the azimuth of the LOP of the lop
itself, you want that azimuth to the AP to be close to the azimuth to the body (or 180° different.)
You may want to try the law of cosines method again, I posted a keystroke by keystroke sequence for use with a simple calculator having only 3 memories.
It is best not to fiddle with the mirror adjusment screws but to just allow for the IE. But you must make sure that the index mirror is perpendicular to the frame using the side adjustment screw.
--- On Mon, 10/10/11, Randall.F.Morrow@kp.org <Randall.F.Morrow@kp.org> wrote:
From: Randall.F.Morrow@kp.org <Randall.F.Morrow@kp.org>
Subject: [NavList] Re: The new guy on the horizon...
To: NavList@fer3.com
Date: Monday, October 10, 2011, 12:54 PM
On artificial horizons:
Having been frustrated
but both the lack of star reflections in liquids and the difficulty of
leveling a mirror, I watched Nav-list for helpful comments and enjoyed
the lively discussion that ensued. Mercury seems to be ideal but
very expensive and almost impossible to acquire due to environmental regulations.
I have made an aluminum, three screw leveling plate with a 6 ½ inch
square first-surface mirror as my a.h.. It is convenient and
wind proof but a not very accurate since my Craftsman digital level is
only accurate to 1/10 degree. A hyper accurate level such as a coincidence
level costs over $1300.00. A Freiberger a.h. runs over $800.00.
Cheaper digital levels run $40.00 and $162.00 for 1/10 degree and
5/100 degree accuracy respectively. I am stuck with the mirror system
for stars but now I use molasses (treacle?) for sun and moon sights.
I level each of the three legs
at least twice, reversing the level by 180 degrees at each leg to get the
most accuracy. The wing-nut head screws have ¼-20 threads with a
90 degree, (1/4) rotation giving 1/10 degree change. When I rotate
the level 180 degrees it takes about 1/8 turn to get back to zero.
The digital level is easier to see in the dark compared to the standard
torpedo spirit levels I started with. No flashlight required.
On intercept distances:
From 7/30 to 10/9
I have performed and reduced and plotted over 400 observations of the sun,
moon, Jupiter and 22 of the navigational stars, but with mixed results.
Most of these were done with my leveled mirror. I have had
intercepts as small as 0.5 nm but more often than not they range from 5
to 25 miles. The LOP accuracy does not seem to correlate well to
intercept distance, as I have had LOP’s that run right over my location
with “a” of 22 miles and some way off with much shorter intercepts.
(I don’t own a GPS unit so I got my Lat.-Lon. from a web site using my
address.)
On sight reduction methods:
I use pub. 229 for
sight reductions. My actual position is about 35* 20’ N and 119*
5’ W. I will use 119* xx’ for 0-30 minutes GHA and 118* xx’ for
30-60 minutes GHA, to arrive at whole # LHA within 30 minutes of my AP,
as suggested in Dutton’s. Is this correct? I have
tried direct solution using law of cosines but found it much more tedious
and error prone than just using the tables. I use a cheap, very
basic calculator. I use a sight reduction form that I adapted from
examples in Dutton’s and Hobbs texts.
On index corrections:
My sextant is a 25+
year old Davis Mark 15 with micrometer drum. I am the sole owner;
it just stayed in the box a long time. Rather than doing index corrections
using the sun and counting on that number to be the same after sunset,
I always adjust out the IE with the screw on the horizon mirror at the
start of each round of sights. The outside screw takes out the IE
and then I adjust the inside screw for side error. Is this correct?
On time:
I love my watch, a
cheap radio-resetting digital by Casio that cost less than $30.00. My
watch error entry is always zero.
My thanks to all for sharing your
knowledge and experience. I look forward to checking my e-mail for
Nav-List posts.
Randy
Randall F Morrow PT
Senior Physical Therapist
Ergonomics Safety Consultant
Chronic Pain Program
Department of Physical Medicine
Kaiser Permanente - Kern County - Bakersfield
Phone: 661-852-3677 (Tieline - 378)
Fax: 661-852-3516 (Tieline - 378)
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