NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars with SNO-T
From: Frank Reed CT
Date: 2004 Oct 27, 20:53 EDT
From: Frank Reed CT
Date: 2004 Oct 27, 20:53 EDT
Alex E wrote:
"But do you agree that that bad observation HAD to be rejected?
It was evident to me immediately when I read my sextant.
My reason and all what I know about statistics imply this."
You didn't reject it. You wrote it down! :-) I frequently reject observations "on site". My eye tears up, my arm gets tired, I get bored... Some such thing occurs that tells me to start over. This is a rejected observation. Is that proper scientific procedure?? I don't care! But I do think that it has been a standard feature of real navigational procedure since the earliest mariners...
After observations have been recorded, and data analysis has begun, keeping or rejecting observations is simply a matter of judgement. As I noted in an earlier thread, the greatest risk is fooling one's self. Do we subconsciously drop observations for the wrong reasons? Or is it true that our gut instincts about bad observations may have some value? Once again, it depends on what you're trying to show when you shoot lunars. What will you do with the results? What are they for? If you're trying to learn about historical navigational practice, then you need to think like a 19th century navigator. How did they feel about observational error back then? What criterion would they use to reject a data point? And if historical practice is of interest to you, be sure to try some lunars on windy days and when the thermometer starts to fall, and if at all possible, from the deck of a vessel on open water. With your teeth chattering and your sea legs weak, your accuracy may begin to fail!
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"But do you agree that that bad observation HAD to be rejected?
It was evident to me immediately when I read my sextant.
My reason and all what I know about statistics imply this."
You didn't reject it. You wrote it down! :-) I frequently reject observations "on site". My eye tears up, my arm gets tired, I get bored... Some such thing occurs that tells me to start over. This is a rejected observation. Is that proper scientific procedure?? I don't care! But I do think that it has been a standard feature of real navigational procedure since the earliest mariners...
After observations have been recorded, and data analysis has begun, keeping or rejecting observations is simply a matter of judgement. As I noted in an earlier thread, the greatest risk is fooling one's self. Do we subconsciously drop observations for the wrong reasons? Or is it true that our gut instincts about bad observations may have some value? Once again, it depends on what you're trying to show when you shoot lunars. What will you do with the results? What are they for? If you're trying to learn about historical navigational practice, then you need to think like a 19th century navigator. How did they feel about observational error back then? What criterion would they use to reject a data point? And if historical practice is of interest to you, be sure to try some lunars on windy days and when the thermometer starts to fall, and if at all possible, from the deck of a vessel on open water. With your teeth chattering and your sea legs weak, your accuracy may begin to fail!
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
