Solve this:
Q.11. How is the zero error of a screw gauge determined?

Zero error : When the fixed stud A and movable stud B are brought in contact without applying any under pressure , and the zero of the circular scale does not coincide with the reference line, there is a zero error.

Positive zero error: If zero of the circular scale is below the base line of pitch scale then error is positive zero error or negative correction as shown in fig. (a) & (b).

Negative zero error: When zero of a circular scale is above the base line of the pitch scale then error is negative zero error or positive error as shown in fig. (c).