# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Lunar distance accuracy
From: Alexandre Eremenko
Date: 2007 Oct 25, 12:23 -0400

```
Dear Frank,

> Alex often gets annoyed when I say that beginners can get

The main disagreement we have on this matter
is not about "novices". After all, my own very first Lunar
in my life (made shortly after I purchased my first sextant)
and posted on the list, was a PERFECT result.
There is no doubt that "beginners CAN".
In the sense that "some beginners sometimes can".

The main point as I understand it is that we evaluate
the same data very differently. We use different numbers
derived from the same series as indicators access "accuracy".
If the "average error" of some long series of observations
(taken over the preiod of weeks or months, like in
the case of White) is say 0'2, then what does this tell you
Very little, indeed.
In a real-life situation you don't want to risk a chance
of hitting some rocks with 5% probability, do you?

By the way, the measures like "quadratic mean" or
"the most probable error" are also poor measures of accuracy.
My recent analysis of White, Bolte and my own observations
shows that
a) distribution of errors is FAR from normal. Which means
that the usual measures of dispersion cannot be applied.
b) they are especially far from normal in their "tails".
That is there are MORE LARGE ERRORS
than a normal distribution
would suggest.

Indeed, in the 42 observations of White, we have
one error of 0'.8 and 3 errors of about 0'.5
in the distance.

And I say that all available data contain a certain
substantial proportion of such outlayers.
You can call them blunders if you wish.

My 121 observations in spring 2007 are as good as White's.
They contain 13 individual shots with the error 0'.5,
2 shots with the error 0'.6 and one with the error 0'.8.

The error of the average is 0'.0.
The average error is 0'.2. If I believe
that this
0'.2 is a "reliable indicator of accuracy" and then
even multiply it by 2 "for safety", I will
"hit the rocks" 18 times out of 120 !

My experience and all available data show that the errors
cwin the range 0.5 and more are UNAVOIDABLE,
and occur perhaps in 10%
of all observations.
This is the main point of our disagreement.

Alex.

P.S. Bolte, White and my own observations of last spring
are now posted on my web site under
http://www.math.purdue.edu/~eremenko/accuracy.html
I will soon add a digest of Bolte in English,
as well, as my own statistical analysis of
all these observations.

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To unsubscribe, send email to NavList-unsubscribe@fer3.com
-~----------~----~----~----~------~----~------~--~---

```
Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)