25d • General discussion
MENTAL MATH
Reciprocal Headings
A reciprocal heading is the exact opposite direction — 180° away. You'll use this constantly: holding entries, intercepting courses, backtracking, and more. This rule is used almost every single time you fly, especially in IFR scenarios with courses TO and radials FROM, this quick mental math trick will save you so much time and headaches.
+2 -2
Say your heading is 180, add 'two' to the first digit and subtract 'two' from the second digit, so 1 plus 2 is 3, and 8 minus 2 is 6, and we leave the third digit alone, so your answer is 3-6-0 which is the exact opposite heading as 180.
Again, say your heading is 045, lets add two to the first digit and subtract two from the second and we get 2-2-5, which is the reciprocal heading!
If your number starts with a 3, like the heading 327, just do the opposite and subtract two from the first digit and add two to the next one, so we now have 3-2=1 and 2+2=4, leaving the last digit alone and we now have a reciprocal heading of 147!
The math behind this is you want to add or subtract 180 degrees, but to make the math easier you just add 200 and subtract 20, or vice versa (if your number is too big) of subtracting 200 and adding 20 back to it. Lets try some more...
090 - plus two since you cant subtract two from zero, then minus two from the next digit = 270
360 - Since you can't add two, start by subtracting first, and adding second, to get = 180
198 -
307 -
144 -
280 - Sometimes it's literally just easier to subtract 180 from it, don't overcomplicate things
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MENTAL MATH
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