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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

   

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