Reciprocal Headings

When initial heading <180°

Then reciprocal = initial heading + 200° - 20°

When initial heading >180°

Then reciprocal = initial heading - 200° + 20°

Double-2 Rule

Add or subtract 2 from the first digit, then do the opposite function with the number 2 for the second digit. The last digit always remains the same.

Example:

Find the reciprocal of 138°

1(+2)  3(-2)  8

318°

Find the reciprocal of 246°

2(-2)  4(+2)  6

066°