Walkhighlands

Can someone tell me why I should get a different calculation for the Magnetc angle from different web sites. One gives the difference at 1' 3" west. While the other gives a difference of 4' 25" west.
Both for Lat 55.563 N and 6.25W

islayhawk

Grid north verses true north?

Out if interest, does anyone know the magnetic to grid north difference this year?

It depends a little on your location - see http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html for a useful tool (based on July 2012).

Look at the general information section of your OS map at a section called North points...it will state the variance between grid and mag for the publish date as well as stating hw much it changes each year so if your map is a few years old, you can calculate the difference...most here say you should always have your own map...being able to convert grid to mag (and back again if taking back bearings or performing a resection) yourself is just as important...your correction must be based on the map you are using

Hi Islayhawk , as MacCookie suggests one figure is the angle between magnetic and grid north(magnetic angle ) ,eg Islay Airport , 1deg 2 min west (July 2012)
The other figure is the angle between grid north and true /geographic north (magnetic declination) , at the Airport this is 4deg 25min west .
The magnetic / grid angle is the one to use when taking bearings and map reading

Edit
Ooops , that should read 'The other figure is the angle between magnetic north and true ..'

Thanks everybody for your replies. It is the magnetic angle I use and I was thrown by the website giving the Declination. Problem solved
Thanks

Islayhawk

There are alternatives. As Mrs Beaton would have it ~ "First catch your dung beetle...."
http://www.bbc.co.uk/news/science-environment-21150721

The British Geological Survey have a page on their website which allows
you to calculate the current magnetic variation for any part of the uk:

http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html

to make sure for my town just now is( MAGNETIC NORTH IS 3,02 W OF TRUE NORT AND 2.00 W OF GRID NORT) so the changes that I have to enter is 2.00 w on my compass ??THX

ramiro darek wrote:to make sure for my town just now is( MAGNETIC NORTH IS 3,02 W OF TRUE NORT AND 2.00 W OF GRID NORT) so the changes that I have to enter is 2.00 w on my compass ??THX

That's correct, though it's hardly worth bothering with in practice.

That's correct, though it's hardly worth bothering with in practice.[/quote]

Oh, I would bother. Remind me not to follow you in a white out.