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    Re: Impressed with the Raft Book
    From: John Huth
    Date: 2010 Feb 1, 09:29 -0500

    I tried to estimate the uncertainty from this method.   Refraction is definitely one of  them, although there are ways of guesstimating refraction effects that will probably be good to maybe 5 arc-minutes.   If you  don't correct for refraction, you can be systematically off by 30 arc minutes or more.

    The rising and setting angle of the sun can also be a nuisance.  

    Certainly low lying clouds, fog banks etc will be a big issue.

    My estimate was that under ideal conditions one could expect an accuracy of about 20 arc-minutes, but you have to put in a refraction correction - ie. know when to start the clock and when to stop the clock.    

    Doesn't a watch count as an instrument?

    On Sun, Jan 31, 2010 at 10:31 PM, Mike Boersma <mike.boersma@gmail.com> wrote:

    Frank Reed wrote: "But in the real world, the observed times of sunrise and sunset are variable for a number of reasons and those variations will significantly diminish the accuracy of this approach to finding latitude."

    What might these reasons be? Refraction? Clouds?

    "It's certainly not a worthless method, but its accuracy is low."

    This method does not appear to be more or less accurate than other no instrument or crude instrument methods of determining latitude.

    I would be surprised if results by this method were better than 1/2d when attempted under real world conditions.

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