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How to Calculate a Reciprocal Heading

Pilots, boat captains and even hikers use headings to indicate their direction of travel, as indicated by a compass. Headings operate on a 360-degree circle where 0 degrees indicates magnetic north and 180 degrees indicates magnetic south. A reciprocal heading indicates the heading directly opposite, or 180 degrees away from, the heading of travel. Calculating a reciprocal heading without using a calculator simply requires practice and knowing the short cut.

Things You'll Need

Compass

Instructions

- 1
  Determine your current heading by reading the degrees from a compass.
- 2
  Add 180 to the heading if your current heading is less than 180. For example, a heading of 145 degrees would give 325 degrees as the reciprocal. Mentally, you may find it easier to add 200 then subtract 20, or, even more simply add two to the first digit of the heading and subtract two from the second digit. Thus, for 145: 1 + 2 = 3 and 4 - 2 = 2, thus the new heading of 325 degrees.
- 3
  Subtract 180 to the heading if your current heading is greater than 180. For example, a heading of 260 degrees would give 080 degrees as the reciprocal. The short cut here is to subtract 200, then add 20. Thus, for 260: 2 - 2 = 0 and 6 + 2 = 8, giving a reciprocal heading of 080.

Aviation