How is zero error in a screw gauze a
ccounted for?
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On bringing the flat end of a screw gauge in contact with the stud, if the zero mark of circular scale coincides with the base line of main scale, the screw gauge is said to be free from zero error.
But sometimes, due to mechanical error, on bringing one stud (say, stud A) with the other stud (say, stud B) the zero mark of the cirular scale is either below (Positive zero error) or above (Negative zero error) the base line of main scale, then the screw gauge is said to have a zero error.
Take an example. Let the 95th division of circular scale coincides with the base line and total no. of divisions on the circular scale are 100. If the L. C. (Least Count) of screw gauge is 0.001 cm, then the zero error = -(100-95)×0.001 cm which, in turn, is equal to - 0.005 cm.
But sometimes, due to mechanical error, on bringing one stud (say, stud A) with the other stud (say, stud B) the zero mark of the cirular scale is either below (Positive zero error) or above (Negative zero error) the base line of main scale, then the screw gauge is said to have a zero error.
Take an example. Let the 95th division of circular scale coincides with the base line and total no. of divisions on the circular scale are 100. If the L. C. (Least Count) of screw gauge is 0.001 cm, then the zero error = -(100-95)×0.001 cm which, in turn, is equal to - 0.005 cm.
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