# NavList:

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

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Re: Cocked hats, again.
From: Peter Fogg
Date: 2007 Mar 21, 07:19 +1100

``` Nicol�s wrote:

> The standard deviation is only predicting 68% of the error (assuming it
> is Gaussian). So if the standard deviation is for instance 20 arcseconds
> it only means that there is a 68% chance (or 68.27% to be more precise)

Or about 70% to be imprecise!

> that the observation is within 20 arcseconds of the actual position. In
> order to get 95% probability you need to multiply the standard deviation
> by 2 (or 1.96 to be accurate, 2 will give 95.45%),

Again, I kept it simple at about 90%

Nicol�s, thanks for implicitly confirming my general idea: that by
constructing these shadow LOPs the larger shape can offer an
overwhelmingly large chance of containing the position, rather than
the alleged 25% chance offered by the original LOPs. The other general
idea I am hoping to show is that the position is overwhelmingly likely
to lie close to the LOPs; each LOP is an approximation of the
position.

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