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Question
Solution
(a) Positive zero error
When two jaws are in contact, the zero of the vernier must coincide with the zero of the main scale. If this is not so, the instrument has zero error. These are of two types:-
a. If the zero of the vernier scale lies to the right of the zero of the main scale then it is called a positive zero error.
b. If the zero of the vernier scale lies to the left of the zero of the main scale then it is called negative zero error
To determine the zero error, note the vernier division coinciding with any main scale division when two jaws are completely closed. Suppose nth division is coinciding with the main scale. Multiply this with the least count of vernier caliper.
Positive zero error = n × L.C.
Negative zero error = - (10 - n) × L.C.
To get the correct reading, the zero error is usually subtracted from the observed reading with its proper sign
Correct reading = observed reading - zero error
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