[time-nuts] Standards for units

[Dr Bruce Griffiths]

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.)
>
> I find the standard for the Ampere, mentioned in the nist  pages above more
> difficult, as 2 infinite wires to measure the force between cannot be
> found! Was the coulomb the standard before? Does anyone have other web
> pages to recommend?
> (Am still learning about the 1948 changes to electrical units,
> international and absolute volts, etc. Before finding this list, did not 
> think much about the differences, about 500 ppm., with a 3 1/2 digit dvm.)
>
> David D.
>   

David

You may find this link somewhat amusing
http://www.sizes.com/units/miners_inch.htm

If one moved around the various mining fields one could become somewhat 
confused by this unit of measurement.


Bruce