A line of levels has been run from a benchmark of elevation +25.32 m and ends at another benchmark of elevation +25.35 m. The sum of back sights is 18.55 m and the sum of foresights is 18.58 m respectively. The closing error in the survey work is:
1
0.06 m
2
-0.03 m
3
0.03 m
4
-0.06 m