Final answer:
To set a reciprocal heading, turn the compass to a heading that is 180° different from the original heading, which is directly opposite on the compass.
Step-by-step explanation:
To set a reciprocal heading, turn the compass to a heading that is 180° from the original heading. For instance, if the original heading is N 30° W, the reciprocal heading would be S 30° E, because these two headings are directly opposite to each other on the compass rose. When subtracting vectors graphically, like a woman sailing a boat, if she travels in the opposite direction for the second leg of her trip on a perfectly reciprocal course, she will trace back along the same path but in the reverse direction.