What is the reciprocal heading formula when the initial heading is greater than 180 degrees?

What is the reciprocal heading formula when the initial heading is greater than 180 degrees?

• A. INIT HDG + 200 - 20
• B. INIT HDG - 200 + 20
• C. INIT HDG + 180
• D. INIT HDG - 180

Answer: (B)

Opposite heading is found by adding 180 degrees and wrapping around at 360. When the initial heading is greater than 180, adding 180 would push you past 360, so you wrap by subtracting 360—equivalently, you can subtract 180 from the initial heading. That makes the reciprocal heading equal to INIT_HDG − 180 in this case. For example, starting at 210 degrees: 210 + 180 = 390, and 390 − 360 = 30 degrees; same result as 210 − 180 = 30. The arithmetic form INIT_HDG − 200 + 20 is just another way to express subtracting 180, so it yields the same reciprocal when the heading is above 180.

Opposite heading is found by adding 180 degrees and wrapping around at 360. When the initial heading is greater than 180, adding 180 would push you past 360, so you wrap by subtracting 360—equivalently, you can subtract 180 from the initial heading. That makes the reciprocal heading equal to INIT_HDG − 180 in this case. For example, starting at 210 degrees: 210 + 180 = 390, and 390 − 360 = 30 degrees; same result as 210 − 180 = 30. The arithmetic form INIT_HDG − 200 + 20 is just another way to express subtracting 180, so it yields the same reciprocal when the heading is above 180.