The staff reading at a distance of 80 m from a level with the bubble at its centre is 1.31 m. When the bubble is moved by 5 divisions out of the centre, the reading is 1.39 m. The angular value of the one division of the bubble, is

ANS:B - 41.25 secs

We know angular value, α =( S/nD) * 206265.

Here.
S = Staff intercept = 1.39 - 1.31 = 0.08 meter.
n = number of division given for change in reading = 5 divisions.
D = linear distance between instrument and Staff = 80 meter.
& multiplied by 206265 to convert an angular value from radian to seconds.

Put the values and answer will be 41.253 seconds per division. 1 degree = 3600 sec.
1 radian =180 degree =57.2958°.
1 radian = 206265" second. 206265 = s/d.

s = 1.39-1.31 = 0.08 m/5 div.

= (206265*0.08)/80.

= 206.265 sec/5 div.

= (206.265*1)/5.

= 41.253 sec/1 div.

Answer B.