Ex24-2 The horizontal angle observed at a theodolite station by a subtense bar with vanes 2.0 m apart, is 0° 30'. Find the horizontal distance between the theodolite station and subtense bar.
If the bar is 1° out from the normal direction to the line of sight, determine the error in the measurement of horizontal distance.
Figure Ex24-2
Solution :
Referring from Figure 24.5, given s = 2.0 m; q = 30', Then from
The horizontal distance between the subtense bar and the theodolite,
Referring figure Ex 24.2,
Therefore Error in horizontal distance = D - D'
= 229 .18 - 229.145 = 0.035 m