Back Bearing

The bearing of the line measured in the backward direction (i.e. opposite to the direction of progress of survey) is called back bearing.

Back Bearing = Fore Bearing ± 180°  

Using a back bearing to identify your position when on a Line Feature

Point the compass at an easily identifiable feature, e.g. the summit of a prominent hill, some farm building, a corner or edge of a forest etc. Turn the Compass Housing until the Red End of the pointer lines up with the Red End of the needle. To get Grid North, deduct the magnetic variation (currently approx. 3 degrees). Place the compass on the map and rotate the whole compass until the lines in the compass housing are parallel to the vertical blue grid lines on the map. Do not move the compass housing. Slide the compass so that one of the long side touches the feature you took a bearing from, taking care to keep the lines in the compass housing parallel with the map’s grid lines. Draw a line along the edges of the compass from the summit to your line feature, where the line crosses line feature is your position.

If you take a bearing on a summit and the compass says its 60 degrees, then the bearing from the summit to your position will be 60 + 180 =240 degrees. Although the compass will line up on your position any way, without adding anything, you can ignore this finery. And also note that a compass only goes up to 360 degrees, so something adding 180 will give you a result higher than 360 degrees.

Identifying your position when not in Line feature by using back bearing 

This is same as the method described in Back Bearing when on line feature, except that you need to take bearings on a least two and preferably three identifiable points lying in different arcs of the compass. Your position will lie where the two or three back bearings intersect or within the triangle created at the intersection.

If you take a bearing on a summit and the compass says its 60 degrees, then the bearing from the summit to your position will be 60 + 180 =240 degrees. Although the compass will line up on your position any way, without adding anything, you can ignore this finery. And also note that a compass only goes up to 360 degrees, so something adding 180 will give you a result higher than 360 degrees.

Questions:

• What is back bearing?
• How to identify the position when not in line feature by using back bearing?