Is there an easy way to remeber how to allow for magnetic deviation? I know that deviation changes based on geographic location and is changing over time but not how the +/- and east/west changes work. What I am looking for is a way to include this information on a card in a PSK.

East is Least (-) and West is Best (+)

>Is there an easy way to remeber how to allow for magnetic deviation?

This is going back into my boating training... might be a little foggy, bear with me...

Often, when people talk about "deviation", they're actually talking about "variation". I think that's probably what you're asking about. On most maps and charts, there will be a compass rose of some sort that will show magnetic and true north. The difference between them is the local [color:"blue"]variation[/color] at that point on the chart.

For example, here in Massachusetts, on the coast, I have a nautical chart that shows a variation of 15 degrees 45 minutes West. When my boat compass is reading North (magnetic), my boat is actually facing west of True North. I'm on a heading of 344 degrees 15 minutes true, even though the compass says 0. I subtracted the variation from the magnetic heading to figure out my true heading.

[color:"red"]A general rule of thumb for variation is this:
Think of variation as an error in your compass relative to finding True North. You want to correct that. If the variation is East, you add it to arrive at true north, Think CAE, Correct Add East. If it's west, like my example above, you subtract. [/color]

Deviation, is normally used to refer to the influence that electronics, wiring, and other magnetic objects have on what your compass will read. On a ship, where most of the things that might affect the compass are in a fixed location, there are methods for determining deviation. For the most part, in the wilderness, deviation is assumed to be zero if you take your compass readings away from metallic objects and electrical influences.

For instructions in a survival kit, you might not want to even worry about deviation, other than saying you should take readings away from metalic objects. For variation if they have a chart, it probably has magnetic north on it, so they can use that when plotting their courses. Half the time, in survival situations, I'd think that the compass will be used to just keep them going in the same general direction, rather than a specific one. They may not even have a map.

Sorry for the long winded answer, I'm sure there are some details I left out that someone else can fill in. I don't know the rule of thumb elsewhere, but, in the US, there is something called the "Agonic Line", where variation is zero. It runs from the North geographic pole, through the North Magnetic pole, and down through the US through a point west of Tampa, FL. Anywhere east of that line has a West variation, and if you're west of that line, you'll have an East variation. Fun eh?

There are a couple places that do a nice job of getting into the details of this. I have done a lot of hiking and orienteering , but, I learned compass and mapping skills originally through boating. Specifically, the US Power Squadron and Coast Guard Auxiliary have some great courses that help with navigation skills on and off the water. A great reference, in a book, is "Chapman's Piloting". It's the bible for boaters. For hiking, I think that several of the outdoor schools do good work with map and compass skills, but, you basically need to get out there and do it when you don't need to, so you're comfortable with it when you do.

I hope you'll share your survival kit info sheet with us when you're done. <img src="/images/graemlins/smile.gif" alt="" />

>East is Least (-) and West is Best (+)

This is probably easier to remember than my "Correct Add East". Someone looking at our two posts might think they were opposites, but, actually, we just were looking at it from different directions.

If you're going from True to Magnetic, the "east is least -" works. If you're going the other way, from a compass bearing to a true north bearing, it's the opposite, which is what I was illustrating.

I think they taught us the concept of "correcting" the compass bearing, (Correct Add East) to help us keep straight whether we were going from magnetic, (which must be corrected for variation) to true,(which is, well, true). Keep smilin.

Yah, I'm going from a flying background, where we steer by a magnetic course. You draw your course on the map, measure true course, then correct it to magnetic and steer that.

In the Marine Corps, we use Right Add, Left Subtract. Meaning, if the deviation is to the right, you add it to your grid, or map direction, and subtract it, if it is to the left. Also, some maps have it listed right near the declination diagram.

http://www.geo-orbit.org/sizepgs/magmapsp.html

I guess I just cheat because if I need to be that precise I used an adjustible compass and set it ahead of time for the area that I will be using it in.

Be sure to update it every few years as the magnetic north pole is on the move! See Earth's Inconstant Magnetic Field on the Science @ NASA website. <img src="/images/graemlins/crazy.gif" alt="" />

Thats exactly what I was looking for. I just started the additional sheets to include in the kit. It's to supplement/correct the information on a set of the Brunton cards. The sum information on direction finding in these is instructions on how to float the disk compass. Actual direction finding is summed up as "REMEMBER: The "N" points north". Nothing about the other methods such as stick & shadow or analog watch.

Your right about the usual use of the compass to maintain a general direction of travel. I ran across an illustration of the effect of only a couple degrees of variation combined with detours around obstacles can have in the woods. I don't remember the distances involved (they were relatively short) but they would have been the difference between a night in the woods on short supplies. The example was a camp located on a creek and traveling to a location and back. You could have found the creek without much problem but once you found it, do you go upstream or down?

Thanks for all the replies. This was exactly what I was looking for.