NavList:

There is a quote in Duttons that Captain Weems made 10 horizon sights on six occasions with an average error of 2 miles and a maximum error of 4 miles. Duttons does not explain how he did this. He must have had extremely good conditions.

Gatty speaks of accuracy of between 6-10 miles with his tables. Again, under ideal conditions, he probably is correct. I was impressed that the theory gave ball park accuracy to begin with.

Under real world conditions (obscured horizons, uncompensated refraction error, non-standard atmospheric conditions, etc.) I would think that at best a novice navigator using nothing but a watch and Gatty's tables could get results within 30 miles for latitude under ideal conditions by timing the length of day.

The only advantage that this method has is that it can be done without instruments. This method should only be a backup to some more accurate method of determining latitude.
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