Why in a traverse does a surveyor often measure distance and

Why in a traverse does a surveyor often measure distance and zenith angle from 1 to 2 and from 2 to 1?

a) coordinates cannot be calculated if both are not measured

b) it eliminates the need to measure height of instrument and height of target when elevations are desired

c) it eliminates the problem that elevation difference is + in one direction and negative in the other

d) it is a check on horizontal distance and elevation difference (2nd only when height of instrument and eight of target is measured

Solution

In the traverse distance and zenith angle is measured twice because:

Answer is D I provides a check on the values. In the data sheet provided with two space. The distance should be measured twice and reported in sequence one above and one below for easy judgement of error in measurement. It is most necessary if the traverse is OPEN.