Zero errors are one of the most commonly occurring errors in measuring instruments such as vernier calipers. A vernier caliper zero error occurs when the vernier caliper is set to its closed position, i.e with the measuring jaws in contact with each other but the zero on the vernier scale does not match with the zero on the main scale, that is to say the reading is not zero. Zero errors can occur due to improper vernier caliper calibration or as a result of mechanical shock which disturbs the alignment of the jaws.
Positive Zero Error
A positive zero error is when the zero mark on the vernier scale lies ahead of the zero mark on the main scale in the closed position, i.e the reading is greater than zero or positive. For example if the reading is 0.1 mm then it is said that the caliper has an error of +0.1. To eliminate positive zero error the zero error should be subtracted from the total reading. For example if the total reading is 3.56 cm and the error is +0.05 then the actual reading would be 3.51 cm.
Also read: Vernier Caliper – Zero Error
Negative Zero Error
Similarly a negative zero error is when the zero mark on the vernier scale lies before the zero on the main scale when the caliper is closed. In other words the reading is less than zero. Negative zero errors can be taken care of by adding the value of the error to the total reading. For example is the total reading is 3.56 cm and the zero error is -0.05 then the actual reading will be 3.61 cm.