At what condition the screw gauge dors not have zero error

The screw gauge doesn’t have a zero error when the zero of the main scale coincides with the zero of the vernier scale or circular scale.
 In case they don’t coincide then the instrument screw gauge is said to have a zero error which can be positive zero error or a negative zero error. In order to get an exact measurement, the error is added or subtracted from the value measured.

Ive never heard of creep meters