[time-nuts] Standards for units

Chuck Harris cfharris at erols.com
Mon Apr 2 09:16:43 EDT 2007


Chuck Harris wrote:
> David Dameron wrote:
>> Hi all, 
>> I just realized that a meter is defined by the speed of light., see
>> http://physics.nist.gov/cuu/Units/meter.html
>> It is only to 9 significant digits, so if the speed of light (in some
>> controlled environment) is measured more precisely than this, the meter and
>> all other derived length units will change?
>>
>> (I was taught that 1 meter was 39.37 inches, to define the inch
>> , but now I see more of 1 inch = 2.54 cm, as someone just referred to.)
> 
> 1 meter/39.37 inches = 0.02540 meters/inch = 2.54 cm/inch = 25.4 mm/inch
> 
> Exactly.

As long as exact means within a few parts per million:

1/meter/39.37 inches = 0.025400051 meters/inch ...

> 
> -Chuck Harris




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