Correct option is B
When both jaws of a Vernier caliper are in contact (i.e., the caliper is fully closed) and the
zero of the main scale does not align with the zero of the Vernier scale, the caliper is said to have a
zero error. Zero error occurs due to improper calibration, wear and tear, or manufacturing imperfections in the caliper.
Zero error affects the accuracy of measurements and must be accounted for by adding or subtracting the error value from the measured reading.
