A student is using a sextant having a Vernier scale. 18 divisions of the main scale of the sextant coincide with 20 divisions of the Vernier scale. If the smallest division on the main scale is 0.1°, then what is the least count of the instrument?

Given

No. of  Vernier Scale divisions VSD= 20

No. of Main Scale divisions MSD =18

Value of one Main Scale Division = 0.1mm

Value of each VSD =  (No. of VSD/ No. of MSD) x  (Value of 1 MSD).

 =  >  (20/18 )X 0.1

 =>  0.11

Least Count of the Instrument =

1 MSD - 1 VSD =  0.1 - 0.11 = 0.01 mm.