So if a tape measure is old it doesnt reflect changes in measurements?

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  • 1 month ago

    the difference is less than the line width of the marks on a tape measure.

  • Anonymous
    1 month ago

    Show me a tape measure that needs changing.  None exist.  What is your problem?

  • 1 month ago

    Whenever we change our definitions it is done so that as far as possible the unit itself does not alter.  This is why the unit of time is such a strange multiple of the frequency of a caesium clock.  The second itself should not significantly alter even if our method of identifying it does. 

  • Anonymous
    1 month ago

    Yeah, I have a heck of a time with my old tape measure which is in centi-cubits.

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  • 1 month ago

    In 1866, the U.S. foot was defined by 1 foot = 12 / 39.37 meters, which implies 1 inch = 25.4000508 mm. By 1930 or so, the "industrial inch" was 25.4 mm. Then in 1959, the U.S. made this the legal definition; the old definition would be called the "survey foot" (to keep the accuracy of old land surveys).

    The practical definition of the meter has changed a few times, such as in 1889, 1960, 1983, and 2019. All of these these changes have been at the level of 1 part in 100 million or smaller.

    Unless you are using a high-accuracy calibrated tape measure from before 1930, or high-grade Johasson gauge blocks, you would never be able to notice the difference.

  • 1 month ago

    Very few tape measures are prepared in an old system that is no longer used.  Minor relatively recent changes in the precision of base units does not have a measurable effect on the scale of any tape measure.

  • 1 month ago

    To the extent that the definitions of length measurements have changed, a tape measure is not precise enough to tell the difference.  For example, about 60 years ago the US survey foot was abandoned in favor of the international foot, but the difference is 1 part in about 500,000.  No ordinary tape measure would detect the change.  

  • 1 month ago

    What changes?  An inch has always been an inch.

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