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I think Frank has done a fine job of putting boundries on its usefulness.  The 
further away from local noon you get, the less reliable it becomes.

The exceptions I take are with the notion that that it is no more accurate 
than just guessing which way is south and that an inaccurate indicator is 
without use.

I have personnally used it to get out of the woods.  The issue isn't about 
late in the day or early in the day.  Even I have a clue about where the sun 
rises and sets.  It's about those six hours in the middle of the day where 
the sun is high and the damned road has manged to get itself lost.


-----Original Message-----
From: Dan Allen 
Sent: Feb 12, 2004 10:54 PM
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Re: Watch into Compass?

On Thursday, February 12, 2004, at 07:45 PM, Frank Reed wrote:

> "I think the accuracy is much better, probably within five degrees and
> most of that is from casually pointing the tiny watch hand at the
> bright spot in the sky."
>
> Sometimes yes, but other times, no way. You should also try it
> "double-blind" sometime. Find yourself a kid "who doesn't know any
> better" and teach the trick. Then go out somewhere, spin said kid
> around until dizzy, and then try to have the kid find the compass
> directions. No coaching! How far off are you and your navigational
> guinea pig?
>
> Until you have procured your guinea pig, consider this: in most of
> June and early July, the Sun's declination is within a degree of 23.
> For that dec, the Sun's azimuth in your latitude (you said 43 N)
> reaches 270, due west, at about 4:10 (-ish) local apparent time. If
> you try the watch trick at this point, it will tell you that South is
> close to azimuth 209. That's pretty far off already. This ignores
> equation of time and zone correction which could easily add another 10
> degree error on top of that. So that's possibly 39 degrees error in
> direction for an observer well away from the tropics. It's worse
> farther south. Yes, it's very roughly in the right direction, but I
> think you would agree that it's not much better than you would get by
> guessing. A person who knows the Sun rises generally in the east and
> sets generally in the west wouldn't be much farther off under these
> circumstances than someone using the watch trick. It's not a very good
> compass!
>
> The watch trick works reasonably well whenever the Sun is close to the
> meridian, and it also works reasonably well whenever the Sun stays a
> long way from the zenith. Otherwise it can be waaay off.

Thanks Frank.  This is what I had thought I had heard.  I wonder why
the US still teaches this to its troops then?

Dan


Dave Weilacher
.US Coast Guard licensed captain
.    #889968
.ASA instructor evaluator and celestial
.    navigation instructor #990800
.IBM AS400 RPG contract programmer

   

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