Zero Error and Zero Correction:

         It is a defect in the measuring device (Vernier Calipers & Screw Gauge) & zero error is caused by an incorrect position of the zero point

For Example:

    To find the zero error, close the jaws of Vernier Calipers gently. If the zero line of the Vernier scale coincides with the zero of the main scale then the zero error is zero. Zero error will exist if the zero lines of the Vernier scale is not coinciding with the zero of the main scale.