Thought I’d put this back up as there was a comment at WRSA on the impact of not having a correct declination adjustment.
Originally posted 12 Mar 2016
Comments on the last post on Magnetic Declination disagree with, or at least minimized the importance of magnetic declination with the general feeling that, ” …’15 degrees’ isn’t that much of an error” or, “15 degrees will only result in a little bit of extra walking..,” or “I can get where I’m going…”
Now, I’m sure that guys and gals out there who’ve been hunting in one area or another (no matter how large) all their lives and have well used topographical 7.5 minute maps can get from point A to point B and so on with a cursory look at their map and shooting a general bearing with their compass. The primary tool they use is familiarity with the AO (a good thing) and terrain association with the compass used as a back up. Ergo, they may not think they need to worry about declination. And, in that particular scenario, those making claims like that are most likely 100% correct.
For discussion’s sake, let’s get into a SHTF scenario or some other situation where the person is using a new map and is unfamiliar with the territory. Say running a security patrol with your NPT with the task of linking up with a neighboring NPT at a particular location at a particular time. If the NPT’s in the scenario don’t concern themselves with accurate grid azimuth conversion to magnetic conversion, lives could be at stake, and the link up will most likely not occur.
Experienced navigators backed up by the facts regarding magnetic compasses and the magnetic ‘North Pole’ will quickly tell you that if you don’t account for the local declination, you stand a great chance of not reaching your objective (which may be getting back to your truck or home or reaching and injured person or whatever you can think of) or becoming lost yourself.
If you’re looking on your map and figure you need to take a 78 degree azimuth, and set your compass accordingly, and you haven’t either adjusted the compass for the local declination (difference between Magnetic North and True North, either East or West), you have a proportionate error when you shoot your azimuth (bearing) to start your navigation. Here’s the error factor of being off by various degrees computed to distance from the target:
1 degree of error at 1,000 meters from start point = 17.5 meters off target (or 19 yards)
5 degrees of error at 1,000 meters from start point = 87.5 meters off target (95 yards)
8 degrees of error at 1,000 meters (my AO) start point = 140 meters off target (153 yards)
10 degrees of error at 1,000 meters start point = 175 meters off target (191 yards)
16 degrees of error at 1,000 meters start point = 280 meters off target (306 yards)
21 degrees of error at 1,000 meters start point = 367.5 meters off target (401 yards)
That’s for a 1 click leg (1,093 yards). Now, let’s multiply that to, say, a 7 click straight line walk. Drum roll: 2,572.5 meters off target at the end of that little 7 click jaunt from the start point, not taking into account any additional anomalies you may encounter while trying to walk that perfectly straight 7 kilometer line you drew on your map.
Now, for discussion’s sake, let’s make our walk shorter. We’ll use the maximum variation in the US – 21 degrees East (Washington State) for a short, 3 click walk. Drum roll: 1,102.5 meters/1,205 yards (even backing it down to the declination in my AO, 8 degrees, it comes out to 420 meters/459 yards – almost half a click – which is a LOT in a rural/wilderness environment). Over a click off your target from the get go; drift, deviation, and pace count error haven’t been factored in yet.
That’s where you are; imagine where you will be when you think you’re at the end of your first leg. The mind boggles. For fun in this mental exercise, add a little thing called, “night” to the equation. Now, for added flavor, consider when the map isn’t matching up to the terrain and you’re positive that your on the right azimuth, the disorientation (something that occurs with little notice) that can add to all the things you’re dealing with, and oh yes, human error in our calculations.
So, if you’re serious about learning or improving your land navigation skills, find a good course and go to it. Or join a local orienteering club. If you want to attend ours, here’s the link. It’s going to be in April 2015. One day will be spent on the academics; one day will be spent in the field getting some, “dirt time,” rain or shine.