UKC

Hi,

I have been reading about navigation an dhave got to a point where i am stuck. So i have my map and compass, now i want to setup my compass. I got this information from http://www.magnetic-declination.com/

You clicked here:
Latitude: 53° 22' 27.7" N
Longitude: 1° 41' 47.7" W
Magnetic declination: 2° 37' WEST
Declination is NEGATIVE
Inclination: 67° 56'
Magnetic field strength: 49138.3 nT

So how would i apply this to my compass?
Also why is there different ways of wrighting lat & lon?

Thanks for any help

In reply to oem_uk: The important bit is the declination - this is the difference between true north and the direction your compass points. Most maps indicate (almost) true north so when using a compass with a map you need to adjust any bearings you make to account of this difference. If you are using a map to work out which direction to walk you will need add 2 and bit degrees to get an accurate bearing in your example. This is a very small difference so can probably be ignored. In some places the difference is much larger and can not be ignored.

In reply to oem_uk: helloo chap. Not sure what you mean to setup your compass? magnetic north and grid north should be shown on your map. Im not sure as to why youd use the website other than interest, as your map says it all. not sure what you mean by different ways of writing latitude and longitude.

What exactly are you trying to set up on the compass?

Set your bearing.

Grid to mag = add variation
Mag to grid = subtract variation

However unless your doing really fine micronavigation you rarely need to bother with the variation in the UK. I rarely need it. Just set a rough bearing and off you plod.

In reply to Milesy: Seconded, its usually too rainy to be that accurate anyway.

In reply to oem_uk: Because the magnetic north isn't actually at the north pole and moves around year to year, true north isn't magetic north. This means that depending were you are the variation will be different, ie almost 0degrees at the equator and say 15degrees in Iceland

In reply to oem_uk:
easy rhyme that has almost bit said

Grid to mag add,
Mag to grid get rid

your map should say the variance on the front, along with a date it was surveyed which is the date to work from as it changes per year i beleive

In reply to oem_uk:
alternatively, this is pretty standard m&c stuff so if you went along to a local scout group/ cadet force, im sure theyd teach you (with scouts might even go towards some kind of badge for them)

In reply to oem_uk: I think i was getting confused with the info that i had, all i needed was this - Magnetic declination: 2° 37' WEST

I got it from a website because when i was reading it said you may need to if you map is old.

As some have said its not thaat much of an issue in the uk which i didnt know.

Lastly, i have seen lat & lon written like this and i dont know what the difference is. But these both take me to the same place?

53.374361, -1.696583
Latitude: 53° 22' 27.7" N Longitude: 1° 41' 47.7" W


Cheers

In reply to oem_uk: Long and lat work in units of 60, not decimal units of hundreds. So, 53 and 22x 60ths = 53.374 in decimal notation. As a corollary, 11.15 am (expressed in 60ths) is the same as 11.25 if you choose to express in decimally.

In reply to oem_uk:
Latitude and longitude are traditionally written in degrees, and the subfractions of degrees are minutes and seconds. So, the examples you give, the latitude is 53 degrees, 22 minutes and 27.7 seconds North. You can express this in decimals (so converting the minutes and seconds to a decimal fraction) and you get 53.374361. (Remember that in converting minutes to a decimal, you divide by 60.)

The two sets of latitude and longitude you give will take you to the same place. The negative sign in the longitude shows that it's a longitude to the West of the meridian. (Similarly, if the latitude had a negative, you would be south of the equator.)

In reply to oem_uk:

If your nav requires knowing such precise long/lat and deviation and you are using OS gridlines then make sure you know the difference between Grid and True North as well as Magnetic.

In reply to Gandalf: I always remember it by the map being a smaller version of the world, therefore the bearing is smaller..

In NZ there was over a 20 Degree difference...

In the UK it's no so small that for most general nav work it can be ignored.

In reply to tony: Thanks for this.


The only thing now is why do you write them differently? Is there a spefic use for either or?

Cheers

In reply to oem_uk: I use this website for work when converting one coordinate into another. much quicker than a calculator!

http://www.directionsmag.com/latlong.php

In reply to oem_uk:

Not a definitive answer but using plain old decimals is easier to enter into computers (and easier for me to visualise) than the more traditional minutes/seconds.

In reply to oem_uk: Thanks for the excelent advice again.

Google also calculates it for you too

In reply to oem_uk:
Don't know really. I'd guess that the decimal version is easier to enter on keypads/GPS systems and so forth.

In reply to oem_uk: In UK there is little point in making the correction, it will be less than 2 degs until 2020 and you cannot realistically set a compass to better than 2 degrees.
BUT it can be up to 30 degs in other parts of the world so if you are only in UK then dont worry, if you are going abroad you should check.
Compasses are designed to work in N or S Hemispheres or you can get Global ones.
Have a look at the Silva guide to using compasses:
http://www.silva.se/upload/Catalogues/123_eng.pdf
Ian

In reply to Milesy:

>
Grid to mag = add variation
Mag to grid = subtract variati

All well and good in this country. Not correct for other parts of the world where mag north is east of true north.

As Iain says, most times the variation will not matter much, though travelling long distances in a boat or plane it could matter, though even then, winds and tides could need further much more involved calculations.

In reply to IainRUK:

Eh! In some places it will be bigger - and it is no where anything to do with the sizes of the world and maps.

In reply to MG: I know, of course...but it's easy to remember around here. Like Mag and get rid rhyme, it's location specific. Book on a course and I'll teach you all you need to know...

www.runsnowdonia.co.uk I'll even offer you 10% discount...

In reply to IainRUK:

Well most recently I wanted to know if, on Italian maps, major crevasses are marked indicatively or at their precise locations, as on Swiss maps. Could you tell me that?!

In reply to MG: Shit, You'd better book on...