# What is the zero error if the datum line coincides with four calibration above the zero

Arun
25750 Points
4 years ago
Positive zero error occurs when the '0' marking of the thimble scale is below the horizontal reference line of the main scale. The error is +x mm. To correct the reading, we subtract the error from the measurement.
Vikas TU
14149 Points
4 years ago
Zero error arises when the measuring instrument does not start from exactly zero. Due to this zero error is present in each reading of the measure.
There are two types of zero error: Positive zero error and Negative zero error

Positive zero error:
If the zero marking of the Vernier scale lies on the right hand side of the zero marking of the main scale, then the error is said to be positive zero error. Look at the position of zero of the vernier scale on main scale
Negative zero error:
If the zero marking of the Vernier scale lies on the left hand side of the zero marking of the main scale, then the error is said to be negative zero error. Look at the position of zero of the vernier scale on main scale