Compass FAQs

Compass FAQs

Some Compass and North related FAQs

Compass FAQs 

Compass & North FAQs

Q. Is it really necessary to take account of magnetic variation, given that the value is so small (and decreasing) within the UK?
A1. Taking the example of a map to land bearing and not adding magnetic variation. Assuming that you did walk accurately on the map bearing, the outcome will be that you will not actually reach the destination on the map that you were aiming for, but you will be slightly left or right of it. The error depends on the distance walked, and based on a broad UK magnetic variation of 2° (approx 2012), you will be 3.5 metres out for ever 100 metres walked. That may not sound much, but you'd normally walk on a bearing for a greater distance than 100m. Walking 1km would lead to an error of approx 35 metres. Still not far. However, in poor visibility 35 metres could make a difference to seeing your target or not. You could of course use additional techniques such as aiming-off give you a better chance of arriving at your destination, but for the sake of adding 2° for a map to land bearing, it's much safer to do it than not. 

A2. Aside from the size of error, there is the matter of good practice. Whilst the UK has a negligible variation at present, some other parts of the world have much greater declination that the variation in the UK, and errors over 1km will be much greater. Get used to doing it here, and it'll be second nature in places where you really need it. (In New Zealand, magnetic declination is between 17° and 25°, so you really do need to adjust for it!)

A3. Magnetic variation is constantly changing, so depending on your age and whether you stay in the UK, the amount of magnetic variation will become greater than the broad figure of 2° in 2012. In about 2024 variation will be broadly 0° in the UK but will then begin to reverse, meaning that magnetic north will no longer be west of grid north, but east. In approx 2036 the variation will be 2° east, meaning that instead of adding variation to a map bearing, you'll take it away. Old habits die hard, so best to get in the right habit from the start, especially if you're young, as magnetic variation is here to stay and will become confusing in the years to come. 

A4. If you're in Northern Ireland, magnetic variation is much greater than mainland UK, as the grid system is different (Irish, not British National Grid). Magnetic variation in Northern Ireland is approx 5.5°, which is clearly much more worthwhile taking account of, especially in poor visibility.

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