Define positive zero error and negative zero error of vernier scale?

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Define positive zero error and negative zero error of vernier scale?

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When zero of vernier scale do not coincide with zero of main scale then there will zero error in the vernier calliper.
1 . When zero of vernier scale lies ahead of zero of Maine scale then this is called negative error.
2. When zero of vernier scale lies behind zero of main scale thilen it is called positive error