On 12-10-2009 18:27, Warp wrote:
> Neeum Zawan <m.n### [at] ieeeorg> wrote:
>>         Perhaps they could _change_ the definition to that, but I'm willing to 
>> bet that it's off by a bit from the current definition.
> 
>   AFAIK kilogram *was* originally defined as the weight of 1 liter of water,
> but for whatever reason they changed it to the weight of a specific object
> (I really can't understand why).

Standards are defined on whatever can be most accurately measured. So if 
you can measure distance and light speed more accurate than time you 
define time as a the interval it takes light to cross a certain length. 
If you increase the accuracy of your clock, you might want to define a 
length as velocity times time, etc. At some point the accuracy of 
quasars was approaching our best clocks, if they would have passed that 
we would now have time defined in heaven.
The standard kilogram can be more accurately measured than a liter of 
water. When we are able to count a specific number of atoms of a known 
isotope and weight those with sufficient accuracy that will probably 
replace the standard kilogram. ATM we are not that far, but only just, 
as this article explains.

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