What is zero error of a screw gauge, and how we find it?

Zero error in a screw gauge refers to the error that occurs when the screw gauge does not read zero when it should. This can happen due to manufacturing defects or wear and tear over time.

Here's how you can find the zero error of a screw gauge:

1. Close the screw gauge completely so that the flat end of the screw touches the anvil. Make sure there is no object between the screw and the anvil.

2. Look at the main scale reading. If the zero of the circular scale coincides with the zero of the main scale, then there is no zero error.

3. If the zeros do not coincide, note down where the zero of the circular scale is. This is your zero error.

4. If the zero of the circular scale is below the zero of the main scale, the zero error is positive. If it's above, the zero error is negative.

5. The value of the zero error is the number of divisions on the circular scale that the zero of the circular scale is away from the zero of the main scale, multiplied by the least count of the screw gauge.

Remember, the zero error needs to be taken into account when taking measurements to ensure accuracy.