magnetic north/grid north

In article <[email hidden]>, BrianG
<[email hidden]> writes

Quoted message said:

It's probably 30 years since I used a compass and added 8 degrees from grid
to true north for navigation purposes. Currently what is the difference in
degrees?

It depends where you are in the UK. The grid is only aligned with true
north along the centre line (2 deg west) and either side of that grid
north diverges from true north.

A good indication ca be had from a recent (last 10 years or so) OS map
of the area. That will tell you the value when it was published and the
rate of change so you can estimate the current value.

--

Dominic Sexton
http://www.dscs.demon.co.uk/

BrianG typed:

Quoted message said:

It's probably 30 years since I used a compass and added 8 degrees
from grid to true north for navigation purposes. Currently what is
the difference in degrees?

If you look on the legend of a "current" OS 1:50,000 map the "difference"
figures will be displayed there.
--
McPloppy ©

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On Fri, 24 Sep 2004 14:19:55 +0100, "BrianG"
<[email hidden]> uttered:

Quoted message said:

It's probably 30 years since I used a compass and added 8 degrees from grid
to true north for navigation purposes. Currently what is the difference in
degrees?

if you have a OS map, look at the info at the (top 1:50k (Side 1:25k)
where the three north's are.

It will tell you what the Grid Magnetic Angle (GMA) is some people may
know is as the Magnetic Variation.

If your map is old here is how to work it out.

Year of map - now year = years old
Annual change x years old = change
Old map GMA - Change = new GMA

If using ordinary compass, round it to the nearest whole degree or 25
Mils.

If using something that can take the exact number, well...

--
Dewi,

(remove spin for email)

In article <[email hidden]>, John Laird
<[email hidden]> writes

Quoted message said:

On Fri, 24 Sep 2004 14:19:55 +0100, "BrianG" <[email hidden]>

Quoted message said:

It's probably 30 years since I used a compass and added 8 degrees from grid
to true north for navigation purposes. Currently what is the difference in
degrees?

Depends where *you* are ! Where I am, it is apparently about 3.56 degrees
W, according to http://williams.best.vwh.net/magvar.html

Beware that is the variation between true and mag not grid and mag which
is what the OP asked for and is most useful when comparing to the OS
map.

Depending upon where you are in the grid the difference between grid and
true can vary from 0 (along 2 deg W) to ~5 degrees (grid squares NA &
NF).

--

Dominic Sexton
http://www.dscs.demon.co.uk/

"Dominic Sexton" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

In article <[email hidden]>, John Laird
<[email hidden]> writes

Quoted message said:

On Fri, 24 Sep 2004 14:19:55 +0100, "BrianG" <[email hidden]>

Quoted message said:

It's probably 30 years since I used a compass and added 8 degrees from

grid

Quoted message said:

Quoted message said:

Quoted message said:

to true north for navigation purposes. Currently what is the difference

in

Quoted message said:

Quoted message said:

Quoted message said:

degrees?

Depends where *you* are ! Where I am, it is apparently about 3.56

degrees

Quoted message said:

Quoted message said:

W, according to http://williams.best.vwh.net/magvar.html

Beware that is the variation between true and mag not grid and mag which
is what the OP asked for and is most useful when comparing to the OS
map.

Err no he didn't! He asked for the difference between grid and true. He
should have asked for the difference between grid and magnetic.

For compass bearings and map work you need the difference between magnetic
and grid, as true north is a rather hypothetical construct to someone
navigating with a map (only deals with grid north) and compass (only deals
with magnetic). You wish to get from where you are on the map to somewhere
else on the map. You work out the bearing on the map (wrt to grid north) and
then convert to the magnetic bearing.

--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Quoted message said:

Depending upon where you are in the grid the difference between grid and
true can vary from 0 (along 2 deg W) to ~5 degrees (grid squares NA &
NF).

--

Dominic Sexton
http://www.dscs.demon.co.uk/

In article <[email hidden]>, Bob Mannix
<[email hidden]> writes

Quoted message said:

Err no he didn't!

Fair cop!

Quoted message said:

He asked for the difference between grid and true. He
should have asked for the difference between grid and magnetic.

He got it right in the subject though!

--

Dominic Sexton
http://www.dscs.demon.co.uk/

BrianG said:

It's probably 30 years since I used a compass and added 8 degrees
from grid to true north for navigation purposes. Currently what is
the difference in degrees?

Magnetic variation is roughly 4 degrees here in South Wales. Same in
North Wales. 3 degrees in London. Wonderful thing this GPS.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

Dominic Sexton said:

In article <[email hidden]>, Bob Mannix
<[email hidden]> writes

Quoted message said:

Err no he didn't!

Fair cop!

Quoted message said:

He asked for the difference between grid and true. He
should have asked for the difference between grid and magnetic.

He got it right in the subject though!

Apologies for missing that. So, as well as depending on where you are, it
depends on which map you're looking at (which I guess is sort of the same
thing). The map-v-grid differences surprised me - are the extremes at the
the very north-west and north-east of the country ? That's where I'd expect
the conic or Mercator or whatever projection to be most distorted, but could
be wrong.

--
Team effort: A lot of people doing what I say.

Mail john rather than nospam...

In article <[email hidden]>, John Laird
<[email hidden]> writes

Quoted message said:

Dominic Sexton said:

In article <[email hidden]>, Bob Mannix
<[email hidden]> writes

Quoted message said:

Err no he didn't!

Fair cop!

Quoted message said:

He asked for the difference between grid and true. He
should have asked for the difference between grid and magnetic.

He got it right in the subject though!

Apologies for missing that. So, as well as depending on where you are, it
depends on which map you're looking at (which I guess is sort of the same
thing). The map-v-grid differences surprised me - are the extremes at the
the very north-west and north-east of the country ? That's where I'd expect
the conic or Mercator or whatever projection to be most distorted, but could
be wrong.

The extremes are squares NA in the Outer Hebrides and TG in Norfolk. If
the country were roughly rectangular, like the grid, you would be
correct.

However the centre of the grid is 2 deg w which leaves the north east
coast near the Northumberland / Scotland border. So there is more of the
country further west of the centre than further east - if you see what I
mean.

--

Dominic Sexton
http://www.dscs.demon.co.uk/

"Paul Saunders" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

BrianG said:

It's probably 30 years since I used a compass and added 8 degrees
from grid to true north for navigation purposes. Currently what is
the difference in degrees?

Magnetic variation is roughly 4 degrees here in South Wales. Same in
North Wales. 3 degrees in London. Wonderful thing this GPS.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

Thanks for all the replies. So to be specific. I'm going to be walking in
the Yorkshire Dales. Somewhere between 3 and 4 degrees then perhaps!!

Quoted message said:

BrianG said:

Thanks for all the replies. So to be specific. I'm going to be
walking in the Yorkshire Dales. Somewhere between 3 and 4 degrees
then perhaps!!

Well my GPS gives me 3 degrees for York. Only does round numbers I'm
afraid, but I guess that's close enough for most uses.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

On Fri, 24 Sep 2004 23:38:34 +0100, "BrianG" <[email hidden]>

Quoted message said:

Thanks for all the replies. So to be specific. I'm going to be walking in
the Yorkshire Dales. Somewhere between 3 and 4 degrees then perhaps!!

You shouldn't wander too far off-track with an error of 1 degree :-)

--
Better to be thought stupid than to speak and confirm it.

Mail john rather than nospam...

The message <[email hidden]>
from "Paul Saunders" <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

Thanks for all the replies. So to be specific. I'm going to be
walking in the Yorkshire Dales. Somewhere between 3 and 4 degrees
then perhaps!!

Quoted message said:

Well my GPS gives me 3 degrees for York. Only does round numbers I'm
afraid, but I guess that's close enough for most uses.

I tried to work out what it was here (Keighley) recently and came up
with 3 and a quarter degrees and I don't suppose a few miles further
north will make much difference.

--
Roger Chapman so far this year 64 summits
New - 42 (Marilyns 12, Sweats 5, Outlying Fells 30)
Repeats - 22( Marilyns 7, Sweats 16, Wainwrights 16)

BrianG said:

"Paul Saunders" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

BrianG said:

It's probably 30 years since I used a compass and added 8 degrees
from grid to true north for navigation purposes. Currently what is
the difference in degrees?

Magnetic variation is roughly 4 degrees here in South Wales. Same in
North Wales. 3 degrees in London. Wonderful thing this GPS.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

Thanks for all the replies. So to be specific. I'm going to be walking in
the Yorkshire Dales. Somewhere between 3 and 4 degrees then perhaps!!

Quoted message said:

OS Outdoor Leisure 2 (Yorkshire Dales Southern & Western Areas)

Magnetic north is estimated at 5 deg west of grid north for 1999
decreasing by about 0.5 deg in four years.

Is that copyrighted?

--

Laz

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A foolproof method for sculpting an Elephant:
First, get a huge block of marble. Then, chip away
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