Answer:
Positive zero error: When the jaws of the caliper are closed, the zero mark on the vernier scale is to the right of the zero mark on the main scale. This means that the caliper reads a value greater than the actual value, leading to a positive zero error.
Negative zero error: When the jaws of the caliper are closed, the zero mark on the vernier scale is to the left of the zero mark on the main scale. This means that the caliper reads a value less than the actual value, leading to a negative zero error.