To set a reciprocal heading on a compass, you should turn it how many degrees from the original heading?

Setting a reciprocal heading means determining the exact opposite direction of your current heading. To achieve this on a compass, you take your original heading and add or subtract 180 degrees. This is because a full circle is 360 degrees, and halfway around that circle is 180 degrees, which gives you the direction directly opposite the one you are currently facing.

For example, if you are sailing or diving with a heading of 90 degrees (east), the reciprocal heading would be 270 degrees (west), achieved by adding 180 degrees to 90. This reciprocal heading is crucial for navigation, as it allows you to safely return to your starting point or to navigate back along the same path you have traveled.