Route surveys are commonly run by deflection angles observed to the right or
left from the lines extended, as indicated in Figure 9.2. A deflection angle is not complete without a designation R or L, and, of course, it cannot exceed 180°.
Each angle should be doubled or quadrupled, and an average value determined.
The angles should be observed an equal number of times in face left and face
right to reduce instrumental errors. Deflection angles can be obtained by subtracting
180° from angles to the right. Positive values so obtained denote right
deflection angles; negative ones are left.