NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Instumental error?
From: Alexandre Eremenko
Date: 2005 Apr 19, 19:59 -0500
From: Alexandre Eremenko
Date: 2005 Apr 19, 19:59 -0500
I am still struggling with my SNO-T, trying to determine any instrumental error from distances. (Once George asked: "Did anyone succeed in determining instrumental error of a modern sextant by ordinary observations"? I cite from my memory: still cannot manage the search engine on this list:-( I think I did. My SNO-T sextant has a certifricate, which is filled by +10" everywhere on the arc. But even the seller confirmed that in the last years of Soviet Union, no one really cared to measure and they filled the certificates with random numbers (even did not care to vary these numbers:-) Anyway, here are the result of my last distance measurements as they are. I will appreciate any interpretation of these numbers. Index correction. Always from 0 to -0.2', since October 2004. I do it every time when I do observations. From the Sun or from the stars. The results are consistent. All distances I mention are measured under ideal conditions from my balcony in perfect weather. Lunars are reduced with Frank's calculator, star distances with my own computer program. A light filter is frequently used on the moon at night, an appropriate one on the Sun, and no filter on the stars. April 19 2:00 GMT, 8 measurements of Sirius-Procyon, standard deviation 0.15', maximal span 0.4', distance approx. 25d40' average error +0.5' 2:20 GMT, 7 measurements of Procyon-Capella, stabdard deviation 0.2' maximal span 0.6', distance approx. 51d7' average error +0.4' Same with Galileo scope, average error +0.3' 2.37 GMT, 7 measurements of Sirius-Capella, standard deviation 0.3' maximal span 0.5' distance approx. 65d48', average error +0.6 22:45 GMT 8 measurements of Jupiter-Saturn, standard deviation 0.3', maximal span 0.5' distance approx 81d53', average error 0.0' 23:30 GMT 6 measurements of Sun-Moon distance, standard deviation 0.2' distance approx 127d10', average error +0.8' This is just a sample. My log book is full of similar data, and they are consistent in the average, produced since October 2004. Can anyone help me to interpret this? (In the beginning I thought that this is my technique to blame, but now (after having tried once Bill's new Astra III) I begin to suspect that this is an instrument error. a) it is ALWAYS positive. b) it ranges from +0.2' to almost 1'. c) Sometimes it is almost zero, but rarely. Based on the recent observations I can make the following table of corrections: 25 38 51 65 68 71 82 90 127 -0.5 -0.4 -0.4 -0.6 -0.2 -0.1 -0.2 -0.2 -0.8 Should I attach this table to my sextant box lid as a certificate, and use it? Any comments? Alex.