Question

With respect to a screw gauge, how is zero correction different from zero error?

Answer 1

Zero correction has the same magnitude as that of zero error. However, its sign is opposite to that of zero error. If the zero error is positive (when the zero of the head scale lies above the pitch scale axis), zero correction is negative and if zero error is negative (when the zero of the head scale lies below the pitch scale axis), zero correction is positive.