To determine the elevation of A, the following observations were made…

Question

To determine the elevation of A, the following observations were made in a tachometric survey, the staff being held vertically. The instrument is fitted with anallactic lens and value of constant is100 and R.L of bench mark is 158.025m.

Inst Stn. | Ht.of Inst. | Staff station | Vertical angle | Hair readings

O | 1.44 | BM | $-5^{\circ}40'$ | 1.332, 1.896, 2.460

O | 1.44 | CP | $+8^{\circ}20'$ | 0.780, 1.263, 1.746

A | 1.38 | CP | $-6^{\circ}24'$ | 1.158, 1.617, 2.076