What is a Back Bearing in navigation?
Back Bearing (aka Reverse Bearing or Reciprocal bearing)
A back bearing is the exact reverse of a bearing and is a useful tool in navigation.
For example, if you walked out from your tent for water on a bearing, take a back bearing, and it will lead you back to your tent.
A back bearing is 180 degrees from your original bearing. So, the back bearing of 038 degrees is 218 degrees.
To calculate a back bearing – For bearings 0-180 simply add 180. For bearings from 181 – 359 simply subtract 180.
If you struggle with the maths try adding 200 then subtract 20, or look at the number opposite your bearing on the compass bezel.
Tips for using Back Bearings
A simple tip for using back bearings is to leave your compass set on the bearing you walked out on, and to walk a back bearing simply turn yourself around and align the white south needle in the Red north lines (instead of your usual red needle).
Now your compass will indicate the back bearing, taking you back the way you came.
If you are walking into featureless terrain but there is a prominent feature behind you, you can walk away from it using a back bearing. Draw a line from your destination or attack point to that feature and take a bearing. Now line yourself up so you are on that exact bearing to that feature. By walking on a back bearing of the feature, you can walk to your destination or attack point. Simply keep checking that the feature is behind you on that exact bearing and keep walking on a back bearing away from it.
Remember you have to be careful with the bearing line. The bearing is from the feature to your attack point. Therefore you have to either choose a feature behind you that happens to be in line with your attack point and is cutting through your current location, or move to that bearing.
For example, let’s say the bearing from the feature to the attack point is 218 deg magnetic, which you have taken from the map. The back bearing is 038 deg magnetic. Now set your compass to 038 and walk sideways towards that bearing with your compass pointing towards the feature as you walk. When you have walked sideways and the red needle has swung into the red compass north lines (red Fred is in his bed), you are stood on the 038/218 bearing to/from the feature and your attack point. Now walk towards the attack point keeping the feature behind you on 038 deg magnetic (you are heading 218 deg magnetic).
You may not be lucky enough to have a feature aligned nicely with your attack point of destination. You can still walk on a back bearing from a feature in the general direction of your attack point to get you nearer. By using a back bearing and measuring your distance travelled, this will give you an estimated position on that back bearing line. This EP now puts you nearer your attack point and you can now take a bearing from your EP to the attack point. By getting nearer your attack point by using an exact back bearing, will have reduced your potential error. Not ideal – but better than nothing.
Back bearings are also useful in relocation or resection to find your position by taking 3 bearings from features and drawing their bearings onto your map. Where the three bearing lines intersect is your current position.
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