Online Ordnance Survey Compass Application

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Delete this post Submitted by Gerald Martyn on 03/Sep/2017


I think this website should be treated with extreme caution as it is misleading:

When adjusting the compass for magnetic declination it pictorially rotates the entire unit, base as well as dial. This makes no change to the actual bearing to be walked by compass. It should rotate the dial, leaving the base along the proposed route as is done in real life.

The magnetic declination used appears to be taken from true north and not grid north. This is incorrect when aligning your compass to an OS map grid. For information, compared to OS grid north the magnetic declination across most of the UK is presently (it does move) less than one degree and in south western areas at least is more or less zero and can be ignored. If in doubt then check the information given on your paper OS map.

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