i. An instrument this is used to measure the thickness of objects like a clipboard, wooden strip is under observation for a specific scenario. Instrument has a pitch of 0.7 mm and a circular scale with 77 divisions is used to measure the thickness of a thin sheet of plastic. Just before the experiment, it was observed that the two jaws of the instrument are brought in contact, the 75th division overlaps with the main scale line and that the zero of the main scale is barely visible. What is the thickness of the sheet if the main scale reading is 0.9 mm and the 39th division coincides with the main scale line?
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Negative zero error = 1/55 mm
Explanation:
Least count of the instrument = Pitch / circular standard deviation
= 0.7 / 77
= 7 / 770
= 1/ 110 mm
Given that the jaws are in contact when 75th division overlaps with the main scale. So the instrument has negative zero error.
Negative zero error = LC * (Division overlapping with MSD - CSD)
= 1/110 * (75-77)
= 1/55 mm
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