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    Re: Test your magnetic compass.
    From: John Huth
    Date: 2012 Nov 15, 14:20 +0100
    I also have done much the same thing with topo maps.   On a 1:24,000 scale, if I take a bearing at an object that's a mile or more distant, I can use a protractor and set of parallels to compare.

    There's an "on the go" trick I use with my topographic maps and nautical charts.   I draw in lines of magnetic variation spaced by statute miles (topo) or nautical miles (chart).    That way, when I take a bearing, I usually just reference to local magnetic north to compare to the chart.   If I want to get a range, I use a string stretched between two points and then stretch the string perpendicular to the lines of magnetic field.   

    This makes coastal piloting and topo map work relatively fast.   When I'm bouncing around in a wind-blown chop in a sea kayak, it's good to have easy and reliable ways of doing routine navigation.



    On Thu, Nov 15, 2012 at 12:37 PM, Apache Runner <apacherunner@gmail.com> wrote:
    Here's how I test my handheld compasses - google earth can give you pretty accurate estimates of bearings, certainly to better precision than a magnetic compass.   

    I take bearings from a known location and then compare these with the bearings from google earth.   That's how I got my estimates of +/- 5 degrees with a cheap handheld backpacker compass.   


    On Thu, Nov 15, 2012 at 12:30 PM, Byron Franklin <byronink@netzero.com> wrote:

    This is part of an old trick to correct magnetic compass on a boat. Head to a buoy, read the compass, add 180 degrees, put buoy on your stern and head away, read the compass, it should be the added 180 this difference gives the amount of compass error. Move magnets or adjust the compass to ½ the found error. See what your compass reads!
    Let me know what you think.
    Byron: Above should have read, This is the amount of deviation of compass error. with no boat this should be very small and perhaps just in your compass.
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