Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Baseplate Compass - Adjustable Declination or No?

Options
  • 25-06-2013 11:50pm
    #1
    7ofBrian
    Registered Users Posts: 1,261 ✭✭✭


    Lads,
    How important is adjustable declination on a baseplate compass?
    As someone who is just learning navigation I dont want to buy a compass only to find out that I need to adjust for declination error on the fly when planning a route.
    Or is it even that important?

    Could someone recommend a compass that will do me for everything i need here? Im moving to canada in feb so id need something that could be used over there too :-/


Comments

  • Options
    #2
    Carawaystick
    Registered Users Posts: 8,779 ✭✭✭Carawaystick


    7ofBrian wrote: »
    Could someone recommend a compass that will do me for everything i need here? Im moving to canada in feb so id need something that could be used over there too :-/
    Whereabouts in Canada? if it's near the MNP, you cannot use a magnetic compass, as the mnp moves too much.


  • Options
    #3
    7ofBrian
    Registered Users Posts: 1,261 ✭✭✭7ofBrian


    Calgary. Should be fine. Only a couple of hours from the border with the states.


  • Options
    #4
    Alun
    Registered Users Posts: 21,464 ✭✭✭✭Alun


    If you don't stray too far from Calgary then the magnetic declination will remain reasonably constant, but with a much higher value than what we have here, it's edging close to 15 degrees East in Calgary at the moment. Also, be aware that as you travel eastwards from there, the bigger and sharper the changes, and at one point the declination will actually flip over and change sign.

    Take a look here http://www.ngdc.noaa.gov/geomag/. There's a good map of declination expressed as a contour map, and you can clearly see where you might start to encounter problems. There's also an online calculator where you can find out the magnetic declination for any location.

    Note that this is relative to TRUE north, so you'll also have to find out the grid convergence for the maps you're using and combine the two if you're going to use it to take bearings off the map. I'm unfamiliar with what grid / map datum is used on Canadian maps so I can't give you any advice there I'm afraid.

    Regarding the compass itself, I've never been a fan of the ones with adjustable declination myself. I'm always afraid they'll get knocked out of 'calibration' in my pocket or something, so I prefer to add it manually. Just a personal preference really.


  • Options
    #5
    NathanKingerlee
    Registered Users Posts: 304 ✭✭NathanKingerlee


    From what I'm understanding of your question here are some points.

    1. Magnetic variation is hugely important and needs to be added or subtracted each time you take a compass bearing. If you ignore magnetic variation it can lead to serious consequences, from getting lost to walking off a cliff!

    2. Part of taking a compass bearing off your map is then adjusting for magnetic variation each time you take a bearing.

    3. Each part of the world has a different amount of magnetic variation; and in fact even different counties in Ireland, etc, have a different magnetic variation.

    4. Your map, or possible online/a forum, will tell you what the variation is. It changes slightly each year, so there will be a calculation to be made.

    Can you take a basic compass bearing at present?
    If not here is a quick video clip I had to do for work; just keep in mind though as this video was for complete beginners, variation was deliberately left out: http://tinyurl.com/pdwp6de.

    Hope all this helps, Nathan


Advertisement