How

A back azimuth is very easy to calculate in degrees.  First, shoot your azimuth.  Then, calculate according to the following rules:

IF YOUR AZIMUTH IS

Less than 180 degrees, then add 180 degrees to get your back azimuth

Greater than 180 degrees, then subtract 180 degrees to get your back azimuth

Exactly 180 degrees, or South, then your back azimuth is either 0 or 360 degrees, both of which are, of course, North

Here is a little practice exercise for you:

Azimuth

Back Azimuth

135

292

Why do you need it

The most common need for a back azimuth, in my experience, is reversing a path.  If you have shot an azimuth on a landmark and approached that landmark only to find out that your path will not work, you may need to reverse that path all the way back to your last known point.  You will use the back azimuth to find the exact direction you need to follow to reverse your path.  Pace counting will be very useful here as well because it will allow you to easily return to an exact point.

Another possibility is that you have a very good landmark behind you, and would like to shoot an azimuth on that landmark, and then travel in the exact opposite direction. 

Here are the answers to the exercise above

Azimuth

Back Azimuth

135

135 + 180 = 315

292

292 – 180 = 112

Tags: , ,

Leave a Reply

You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>