A surveyor started a longitudinal section leveling survey by taking starting bench mark of elevation 53.85 m. During the survey, he takes an observation of intermediate sight of 2.42 m with the staff held on another bench mark of 85.45 m. The sum of the back sights from the start to the point is 50.28 m and that of fore sight is 16.30 m. If the surveyor ends the survey operation on the second bench mark, the error of closure on the second bench mark, in m, is __________. (Rounded off to 2 decimal places)
Options:
(A) 0.02
(B) 0.04
(C) 0.06
(D) 0.08
Official Answer Key:
B
Step-by-Step Solution & Explanation
Step 1 — compute the observed reduced level of the second bench mark by the rise-and-fall bookkeeping in its height-of-instrument form:
RL = Starting RL + ΣBack sights − ΣFore sights − (Intermediate sight on the point)
RL = 53.85 + 50.28 − 16.30 − 2.42
= 104.13 − 18.72
= 85.41 m
Step 2 — compare with the known (true) elevation of the second bench mark, 85.45 m:
Error of closure = |85.45 − 85.41| = 0.04 m
Interpretation: the survey has accumulated 4 cm of misclosure over the run; the levels would be adjusted proportionally to distribute this error before the section is plotted.
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.