What is meant by zero error of a vernier callipers? How is it determined? Draw neat diagrams to explain it. How is it taken in account to get the correct measurement?

Draw a neat labelled diagram of a vernier callipers. Name its main parts and state their functions.

Draw a neat and labelled diagram of a screw gauge. Name its main parts and state their functions.

Describe the procedure to measure the diameter of a wire with the help of a screw gauge.