# NavList:

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

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Re: To what level must the accuracy go?
From: Tom Sult
Date: 2018 Oct 13, 18:55 -0500
Can one really be 0.5 consistently?  Between index error, refraction error, interpolation error, time error, etc, what is the real limit of reproducibility? From a small boat under 50 feet I am vary happy with 5.

Tom Sult, MD
Author: JUST BE WELL

Hello Kermit

"Let me flip it.  You managed to improve your accuracy, mid ocean, by 0.5NM.  Does it matter?"

You are striving to do your best and to improve in a discipline - CelNav to name it - which is both a Science and an Art.
Nowadays - and for the time being - you can even check your performance anytime and anywhere on Earth.
As you are also enjoying some kind of honestpride through it, does it not matter too ?

*******************

If you and I were on a ship, mid ocean, and independently arrived at a fix using CN no more than 0.5 nautical miles from each other, we both would be quite thrilled and prideful that we had achieved such agreement.  I'd go so far as to extend that figure to 3nm and still be happy. Similarly, comparing my result to a GPS derived position and arriving at a fix to within 0.5 mm, I would be very happy with my skill level indeed.  All possible errors considered, 0.5 nm is terrific agreement.

That is my meaning.  It's more than good enough for navigation, when being inside a permissble error or box is the goal.  Mid ocean, 10nm.  Closer to shore, 3nm.  Being more precise doesn't provide, to me anyway, any more meaningful data.  Once inside that box, examine your chart and look for danger to steer away from.

I'd rather assume my position is closer to the danger, so as to steer away from it, than to more precisely define my position within the permissible error or bounded box.  If there is no danger, than nearly any position within the bounded box will do, there is no advantage to any individual position.  We will both make landfall and switch to coastal piloting, soon enough.

For me CN is to provide a practical result.  I have carefully observed that you care very much for the last bit of accuracy.  That's an admirable level of effort and indeed, achievement.

Exams and licensing are a different beast altogether.  Obtaining the precise result, from the given starting point is relevant to demonstrate mastery of the requested methodology.  Obtaining a numerical value that differs in the last decimal place is cause for alarm.   An arithmetic error may be present.  A sign was manipulated improperly.  A table wasn't consulted, etc.   I have observed your attention to detail here as well.

I hope this explains my meaning a bit better.

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