If the two instrument stations are in same vertical plane as the elevated object and the instrument axes are at same level, then find out R, L of point 'Q', as per given figure,
Where: α1 = angle at instrument at 'P', α2 = angle at instrument at 'R', b = distance between two instruments, D = horizontal distance between first instrument and foot of elevated object; R, L, of B.M. = Reduced level of bench mark as shown in figure.
1
R.L. of B.M. + S - \(\rm \frac{(b\times cos\alpha_1\times cos\alpha_2)}{cos(\alpha_1-\alpha_2)}\)
2
R.L. of B.M. + S + \(\rm \frac{(b\times sin\alpha_1\times sin\alpha_2)}{sin(\alpha_1-\alpha_2)}\)
3
R.L. of B.M. - S + \(\rm \frac{(b\times sin\alpha_1\times sin\alpha_2)}{sin(\alpha_1-\alpha_2)}\)
4
R.L. of B.M. + S + \(\rm \frac{(b\times cos\alpha_1\times cos\alpha_2)}{cos(\alpha_1-\alpha_2)}\)