What is meant by zero error of a vernier callipers? How is it determined? Draw neat diagrams to explain it. How is it taken in account to get the correct measurement?

Sometimes due to mechanical error in vernier callipers, the zero mark of the vernier scale does not coincide with the zero mark on the main scale. Hence, the vernier callipers is said to have a zero error.

In order to find the zero error, we note the division of the vernier scale which coincides with any division of the main scale. The number of this vernier division when multiplied by the least count of the vernier gives the zero error.

For example if the least count is 0.01 cm and the 6th division of the vernier scale, coincides with a main scale division then.

we get,

$\text{Zero Error} = 6 \times \text{L.C.} \\[0.5em] \text{Zero Error}= 6 \times 0.01 \text{cm} \\[0.5em] \Rightarrow \text{Zero Error}= 0.06 \text {cm} \\[0.5em]$

Hence, zero error = 0.06 cm.

In order to correct the measurement of the vernier callipers with zero error, the zero error with proper sign is subtracted from the observed reading.

Hence, Correct reading = observed reading – zero error (with sign)