what does this mean?

Question

magnetic to grid subtract grid to magnetic add

Answer 1

its the difference between magnetic north (Where your compass Points) and the true north (Where the maps show north to be)

the difference is different throughout the world, and a decent map will show the variation on it.

when you take a bearing off the map and apply it to your comapss you must compensate by the required amount.
i.e from map (grid) to compass (Magnetic) add on the variation

and from compass bearing (Magnetic) to map (grid) subtract the variation!!

Answer 2

There are three types of north:
Grid North: the north that the lines on your map point to
Magnetic North: the north that your compass points to (magnetic clump of rock just off the coast of canada.
True North: where the north pole sits

When map reading and you take a bearing from your map it reads a grid bearing to make this as it is on the land and to navigate by you want to convert it to a magnetic bearing. There is a variation between magnetic north and grid north usually about 5degrees though if you have a look on your map it should tell you the current variation as the magnetic rock moves.

To get the bearing from the gird bearing to a magnetic bearing you need to add the variation e.g 5degrees or vice versa if u wan to go from a mag bearing to a grid bearing.

To remeber this just say: "Grid to Mag Add"

Answer 3

I would guess this is on a map of some sort.

It is giving you the adjustment to make if you want to switch between magnetic and grid north. Grid north is usually striaght up on the map so if you apply the adjustment (ie add the difference given) then you will have the direction of magnetic north and can compare this with the reading from a compass.

Answer 4

both of the above a correct, better to have some demonstrate its easier to see exactly what the mean, but basically magnetic north [gravitational pull](situated some where in canada- i think) changes every year, so you need to check the year the map was printed and take this into consideration when walking on a grid bearing over long distance or you will end up in wrong place (the further the distance, the more mils/KM you will be out

Answer 5

thats how you work out bearings n stuff when navigating

... magnetic (compass) to grid (map) you add,
grid to magnetic subtract.

You've got it backwards.

the way you remember is.... My Great Aunt (mag - grid add)
and..... Grand ma Sucks ( Grid to mag subtract)