![]() You must use a grade-school protractor and a long straight edge placed on the edge of the map (the TN line) to be accurate enough. Extending that short MN line will almost certainly result in error. The USGS will tell you that the angle as drawn is only representative of the actual angle, especially for small angles. ![]() I have over 300 USGS maps in my collection, very many have MN lines on them and I have no intention of throwing them away.īy the way, if using this method do not simply extend the short MN line as drawn on the map in the declination diagram. However, as checked recently, the declination in my area has changed by only a degree to a degree and a half over all the years I have been using the method, so even my early drawn maps are still quite useable. ![]() It is true that the declination has changed over time, and the MN pole seems to be in runaway mode in recent years. I have always used the draw magnetic north lines on my maps, especially for my personal backcountery travels. I have taught basic and advanced land navigation for more than 30 years, including to Homeland Security, Law Enforcement, EMS, SAR, and licensed wilderness guides. Henceforth, at least until Magnetic North moves again, you can use the Declination Line(s) to orient the map to Magnetic North, and use the compass without having to consider/adjust for the declination.īack in the day, for maps we used a lot, we'd use a parallel ruler to locate and draw declination lines in several key places on the map. Verify with your compass and you're done. Carefully draw a line back from the dot to the base of the True North line (the spot where the Magnetic North line first branches off).Ĥ. Using the True North line as Zero (obviously), locate the correct degree of Declination on the protractor. Bigger ones are easier to read and use, and therefore more accurate.Ģ. Carefully extend the True North line out far enough that it can be used with the biggest protractor that will fit on the map. Check and verify the current declination before doing this.ġ. ![]() On any USGS map the True North line is always accurate but the Magnetic North line may not be. Unfortunately, what the protractor on the map says and what it measures with other protractors is different. I was thinking of using maps with the drawn in lines so I could use either one interchangeable with the map and not have to remember to add/sub. But the other compass I use a lot is a military lenstatic - no adjustments. My primary compass is a MC2 global, which has adjustable declination. Or if I make notes while traveling, I can easily transfer the notes to the map based on the drawn lines instead of having add/sub declination when transcribing my notes. I can easily orient my map with the drawn lines, shoot an azimuth of 111 and plot my course, without math. I line up on it and see it is 111 degrees from MN. The next place I want to go is a my 4:00 o'clock. Example, I am on a hill and am looking north according to my compass. Also, if you use the marked map and orient it with the drawn lines, it's easier to match? the terrain. ![]() By doing do, you do not have to change the declination or remember to change the declination on your compass (if you can change it). The idea is to draw declination on your map so you do not have to remember to add or subtract when you plot a course. ![]()
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