18) Which is the instrument that can easily be converted to mm/inch measurement?

19) What is the use of ratchet in out side micrometer?

20) Calculate the least count, if 49 main scale divisions are divided into 50 equal parts on the vernier scale?

21) What is the least of an outside micrometer metre having 50 divisions on thimble and pitch of screw in 0.5mm?