What do you mean by zero error of a screw gauge? How is it accounted for?

Name the two scales of a vernier callipers and explain, how it is used to measure a length correct up to 0.01 cm.

Explain the terms —

(i) pitch, and

(ii) least count of a screw gauge.

How are they determined?

A screw gauge has a least count 0.001 cm and zero error + 0.007 cm. Draw a neat diagram to represent it.