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compasses

way over rated!! i use mine fer the mirror!!! that way i can see where i am!!!! :D :eek: :D :eek: :D :eek:
 
Are we really going to take the scientific advice of someone named Stoner :D

well, as long as maps are produced frequently enough and they always update the declinatino on them, it shouldn't matter.

I can't wait until the "polarity" gets reversed again!

then I might end up in Witherle Ravine instead of North Basin...

spencer
 
Most USGS maps actually list the yearly change in declination on them already. Its usually small like 0.1 degree per year. You can read when the map was made or revised and then it is simple math to calculate the current declination. IIRC. I don't acutally have one in front of me. :D They are not updated that frequently. 10 to 40 years is typical with some photo revisions more often in certain areas.

Keith
 
post'r boy said:
way over rated!! i use mine fer the mirror!!! that way i can see where i am!!!! :D :eek: :D :eek: :D :eek:
Click to expand...

You can also see who is lost. ;)
 
I print my maps frpom Topozone. Topozone always lists the current declination, not the one printed on the original maps.

So forget paper maps, go on-line and you're good.

Pb
 
SAR-EMT40 said:
Most USGS maps actually list the yearly change in declination on them already. Its usually small like 0.1 degree per year. You can read when the map was made or revised and then it is simple math to calculate the current declination.
Click to expand...
The accuracy of this prediction decreases with longer time intervals.

Start from the most recent map you can get...

Doug
 
DougPaul said:
The accuracy of this prediction decreases with longer time intervals.

Start from the most recent map you can get...

Doug
Click to expand...


Yes, it can be variable and the rate of the rate of change is not always linear and differs from place to place but (that second derivative) it is usually negligible unless you are using really, really old maps. ;)

Also as well as east-west declination there is what is referred to as "dip" or magnetic inclination. This mass of molten iron is also "sinking" as well as moving from left to right. For the vast majority of us this has no meaning. Just another useless fact rolling around in my head. :eek: :cool: :eek:

Keith
 
Last edited:
Why not do all calculations in MN

This is as good a place as any to throw this out. I seem to have fallen into the habit of simply drawing MN lines on paper maps, or having TOPO draw my maps using NM and never bother with the declination. Saves the trouble of translting from MN to TN and back. Anyone else do this? If not, what am I missing?
 
yardsale said:
This is as good a place as any to throw this out. I seem to have fallen into the habit of simply drawing MN lines on paper maps, or having TOPO draw my maps using NM and never bother with the declination. Saves the trouble of translting from MN to TN and back. Anyone else do this? If not, what am I missing?
Click to expand...


Yes. There is no reason not to do this and it is likely to cause the least amount of problems, especially with novices. Just be explicit when you give someone a bearing that your bearings are MN so that they know. At least that way anyone who is not using mag lines on their map will know how to put bearings on their map. You should always make this part of your bearing anyways. Always state MagNorth or TrueNorth when giving a bearing. The term 28 degrees should not be in anyones vocabulary. It should be followed with either mag or true to be a valid bearing. Thats what I teach. IMHO.

Most of the compasses I have allow declination to be taken out right in the compass so taking a reading from the map is no problem and neither is the conversion. Lines on the map are no problem and help also. Most orienteering maps are already oriented with magnetic north so declination isn't a consideration. They drew the magnetic lines on the map and turned the map so they point towards the top of the map. :D

Keith
 
SAR-EMT40 said:
The term 28 degrees should not be in anyones vocabulary. It should be followed with either mag or true to be a valid bearing.
Click to expand...
That should be 028 degrees mag/true--all bearings/headings should have 3 digits. Reduces the chance of error.

Doug
 
yardsale said:
This is as good a place as any to throw this out. I seem to have fallen into the habit of simply drawing MN lines on paper maps, or having TOPO draw my maps using NM and never bother with the declination. Saves the trouble of translting from MN to TN and back. Anyone else do this? If not, what am I missing?
Click to expand...
Absolutely. I've been doing this for many years, and I teach it in a wilderness guide's course. When at a vista spot it is useful to actually orient the map to the earth, but for general on-the-move navigation the MN lines method lets you navigate quickly while on the move. With this method no math is needed and you don't even need to know the numerical bearing to navigate, it gets taken care of automatically. I'll always glance at it though, having learned the hard way when the dial got turned randomly in heavy brush and I didn't notice the error until some time later when terrain clues didn't make sense.

The added bonus of drawing the lines is it gives you an excuse to do map study before your trip. It only takes a few minutes to draw the MN lines, but spending an hour or two on map study before a bushwhack pays off many times over.
 
yardsale said:
Anyone else do this?
Click to expand...

Well, you have lots of company. The entire worldwide sport of orienteering adopted this as a convention a long time ago. Not only does it save the trouble of switching back and forth, it avoids a major source of embarrassment for participants.

Just be sure that you always specify "magnetic" or "true" when communicating about bearings and headings with someone else. If the response from the other person is "Huh?", I'd find another partner for that long bushwhack ...
 
I love that my map software gives me the option of True or Magnetic. Works well, except when you don't also set the electronic compass in the GPSr to Mag north... Not that I would ever do that, of course, but just in case any of you need to think about that. Not me though, nope, uh uh :eek: Also a good reason to carry a good old fashioned compass. That way you can figure why you are going down when you should be going up. I am speaking hypothetically, of course :rolleyes:
 
mistaking down for up and other minor errors

I suppose we've all been there. A month ago Dave Metski and I met some other list members on a Mountain top. I gestured to the East talking about the view into Tuckermans---Trouble is we were on Lincoln.
 
Don't ask me where the term comes from, but declination is the difference between true and magnetic north reading given by your compass. At a basic level, consider this more or less static for any particular geographic are, but as you can see from this thread, the declination evolves over time as the magnetic poles drift over time. Not a practical problem unless you are manually plotting extreemly prescise routes!
 
John H Swanson said:
What's declination?
Click to expand...
It's what happens to you as you get older. But don't worry about it now, you'll find out soon enough, I guarantee it.
 
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