Question

In order to find the difference in elevation between two points, P and Q, a level was set on the line PQ, 60 m from P and 1280 m from Q. The readings obtained on staff kept at P and Q were respectively 0.655 m and 4.250 m. The difference in elevation between P and Q is

• A. 3.485 m
• B. 3.415 m
• C. 3.748 m
• D. 4.012 m

Answer 1

The correct option is A 3.485 m

Since the distance of P from instrument is small, the correction for curvature etc, is negligible.
Combined correction for $Q=0.06728(1.280{)}^2=0.110m$ (subtractive)
$\therefore$ Correct staff reading at Q = 4.250 - 0.110 = 4.14 m
$\therefore$ Difference in elevation between P and Q = 4.140 - 0.655 = 3.485 m (P being lower)