2001-08-31
They can wiggle all they want. In theory, all FFU can be defined in the
exact same manner as metric ones are. In reality, no! It was already
agreed that FFU would be defined relative to metric units before metric
units were defined by these standards. To change FFU so it is defined as SI
is defined, would actually cause another physical change in the length of
the certain FFU as was done in 1960.
For example:
The yard is defined as 0.9144 m. The metre is defined as distance light
travels in 1/299 792 458 s. If the yard is to be defined the same way, then
it would be the distance light travels in 1/327 857 018.810 148 731 408 573
928 258 97 s. Yes, a long, unending number. If you truncate it to 1/327
857 018, then you in fact lengthen the yard from its present value, even if
it is an extremely small amount. Those small amounts factor in when
speaking of very large distances and create enough error to be noticed. If
you round it up to 1/327 857 019 s, you will in shorten the yard from its
present value. For this reason it is not done.
But again, would it really matter? FFU has changed so often who knows what
is really a true yard, or pound, or whatever?
John
----- Original Message -----
From: "Han Maenen" <[EMAIL PROTECTED]>
To: "U.S. Metric Association" <[EMAIL PROTECTED]>
Sent: Friday, 2001-08-31 01:47
Subject: [USMA:15079] Fw: Questions about measurement standards 3
> See how they try to wiggle their way out of it.
>
> Han
>
> ----- Original Message -----
> From: "John Gardner" <[EMAIL PROTECTED]>
> To: "Austin Spreadbury" <[EMAIL PROTECTED]>; "'Joseph B. Fox'"
> <[EMAIL PROTECTED]>; "mail" <[EMAIL PROTECTED]>; "Han Maenen"
> <[EMAIL PROTECTED]>
> Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
> <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
> <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
> <[EMAIL PROTECTED]>
> Sent: Thursday, August 30, 2001 7:54 PM
> Subject: RE: Questions about measurement standards
>
>
> > As Austin says, inches and pounds are defined (in legislation) in metric
> terms. However, metric is itself defined by so much distance travelled by
> light in
> a vacuum, etc. It therefore follows that the inch and pound can also be
> defined by the distance of light travelled by light in a vacuum.
> Consequently, metric can be defined by imperial units, as well as vice
> versa.
>
> Just because scientists used metric when defining the distance of light,
> there is no inevitable reason why this should have been so. They could
have
> used feet.
>
> So, it's a level playing field when coming to defining one system in
terms
> of another.
> John
