# NavList:

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

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Re: Ratio of variances
Date: 2018 Nov 3, 11:46 -0400
Hello Bill

I think perhaps you are asking for something which we don't know, a numerical value for a confidence level of an individual observation or group thereof.

Those with far more experience than I will state that they "know" when an observation "feels" right or wrong.  Perhaps they are correct, but it doesn't go much further than that.  Could we go as far as a low, medium or high confidence?  Maybe.

I recognize that to further work the symmedian point description, you may need to assign numerical values.  In so far as the moon, the sea that is illuminated by the reflected moonlight often leads to a confused horizon.  The illuminated sea under the moon sparkles in the eye. This may be a possible way to realistically assign a numerical value yourself.  The moon observation could have a medium or low confidence level, due to the confused horizon.

When CN was king, and GPS didn't exist to compare a result, the known uncertainty in a fix precluded these mathematical exercises.  There was no point is fiddling the fix about minutely, as it simply didn't matter.  CN was meant to find your position, mid ocean, in a featureless environment.  Mid ocean, a few miles plus or minus doesn't mean anything.  Close to danger like a pinnacle? Assume you are close, so as to maneuver away.

On Fri, Nov 2, 2018, 10:24 PM David Pike <NoReply_DavidPike@fer3.com wrote:

Bill

Bill Lionheart You wrote:  Can NavList members give a practical example where you might take sights for three or four bodies (average of several sights for each) and suspect that one of them is say half (or some other fraction) as accurate as the others?

How about every navigator’s dream, a Sun, Moon, Venus fix?  It’s not available very often, but when it is, you’d have time to get the shots in.  The Sun would probably be low, so atmospheric refraction might be difficult to calculate precisely, which would affect the band of error.  Also, some navigators never seem to get on very well with the Moon, so that might have an effect.  Of course, confusing Venus with a police helicopter hovering or an aircraft on very long finals would really upset the applecart.  DaveP

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