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    A micrometer, reading to +_ 0.01 mm, gives the following results when used to measure the diameter d of a uniform wire:
    1.02 mm 1.02mm 1.01mm 1.02mm 1.02mm
    When the wire is removed and the jaws are closed, a reading of -0.02 mm is obtained. Which of the following gives the value of d witha precision appropriate to the micrometer?

    A. 1.0 mm
    B 1.00 mm
    C. 1.038 mm
    D 1.04 mm

    First thing to do is to take the -0.02mm offset into account, which means all your readings are bigger than you read off the scale.

    Your readings then become four 1.04mm, and one 1.03mm.

    The average of these readings is 1.038mm. However, since your micrometer is only accurate to +/- 0.01, the 3rd decimal place has no meaning here, and you have to round up to 1.04mm.
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Updated: April 12, 2006
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