The Consequences of Ignoring Declination in Land Navigation Can Kill You...
NOT TAKING LOCAL DECLINATION INTO ACCOUNT WHEN NAVIGATING COULD BE DISASTEROUS
Let's say, for discussion's sake, you’ve plotted on your map and then set a 78 MAZ on your compass and you haven't either adjusted your compass for the local declination or converted your grid azimuth to magnetic by either subtracting or adding the correct declination degrees, depending on where you are in the country. This oversight will cause a proportionate error when you start your navigation that only gets worse as you go along. Here's the error factor of being off by various degrees computed to distance from the target from exact, straight line navigation with no drift whatsoever:
• 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)The example above is for only a 1 click leg (1,093 yards). Now, let's multiply that error by to, say, a factor of, meaning, a 7 click straight line walk.
Drum roll: 2,572.5 meters (2.5 clicks) off target at the end of that little 7 click jaunt from the start point, again, 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. Things like drift, magnetic interference from various items like ore deposits, high tension wires, etc.
We'll use the maximum variation in the US - 21 degrees East (Washington State) for a short, 3 click walk (just about 2 ¾ miles).
Another Drum roll: You’d be off your target by 1,102.5 meters/1,205 yards before you took a single pace! Over a click off your target from the get go in Washington State and drift, deviation, and pace count error haven't been factored in yet, let alone the soon to be fact that you are lost. If you're trying to get to a place with food, water, and friends, depending on the season, the weather might just kill you. If you're navigating through hostile territory, well, use your imagination.
Let’s back it down to the declination 7.5 degrees W, it comes out to 420 meters/459 yards - almost half a click - which is a LOT in a rural/wilderness, hostile weather, or hostile human environment.
Bottom line? Ignoring declination can get you killed. Always check your declination and ALWAYS either adjust your compass (if it's declination adjustable) or perform the addition or subtraction of the correct declination when going from the grid map to the magnetic compass.