### subtract-headings

#### subtract-headings heading1 heading2

Computes the difference between the given headings, that is, the number of degrees in the smallest angle by which heading2 could be rotated to produce heading1. A positive answer means a clockwise rotation, a negative answer counterclockwise. The result is always in the range -180 to 180, but is never exactly -180.

Note that simply subtracting the two headings using the - (minus) operator wouldn't work. Just subtracting corresponds to always rotating clockwise from heading2 to heading1; but sometimes the counterclockwise rotation is shorter. For example, the difference between 5 degrees and 355 degrees is 10 degrees, not -350 degrees.

    show subtract-headings 80 60
    => 20
    show subtract-headings 60 80
    => -20
    show subtract-headings 5 355
    => 10
    show subtract-headings 355 5
    => -10
    show subtract-headings 180 0
    => 180
    show subtract-headings 0 180
    => 180

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