How do you calculate a back azimuth if the azimuth is over 180 degrees?

To calculate a back azimuth when the azimuth is over 180 degrees, the correct method is to subtract 180 degrees from the given azimuth. This is because the back azimuth represents the direction directly opposite to the original azimuth.

When the azimuth is greater than 180 degrees, the compass direction you are facing is in the southwestern quadrant. By subtracting 180 degrees, you are effectively finding the angle that points directly back in the opposite direction. For example, if your azimuth is 250 degrees, subtracting 180 degrees gives you 70 degrees, which is the back azimuth. This method allows you to accurately determine the exact reverse bearing, essential in land navigation to effectively find your way back or orient yourself in the field.