RE: Billions

[Chris Handley <cbmvax!uunet!GANDALF.OTAGO.AC.NZ!cuvmb.cc.columbia.edu!CHandley>]

Colin responds to Ivan

>Point taken. However, I observe that for any particular quantity,
>only a certain range of values (perhaps 6 or at most 12 orders) are
>commonly used. I have never heard anybody use Mm (megametres),
>still less larger multiples; likewise, I have never come across mF
>(millifarads), meV (milli-electron volts) Mg (megagrams) or exa-,
>femto- or atto- anything. Added to which, the two most common
>metric systems each take as one of their fundamental units
>something which appears to be derived (centimetre in CGS, kilogram
>in MKS). All in all the whole thing is a mess.
>
Certainly, much of the system is a mess, the propounders of the
metric system had a reasonable stab at producing some reasonable
sized units, and on the whole did a pretty good job. Their provision
of a large number of prefixes was wise bearing in mind the
possibility (realised) that some units would be too large/small for
normal use.

However, I have seen 1AU described as (about) 150 Mm, and amps,
volts and (to a lesser extent) gauss are routinely quoted from femto
to Giga, and possibly beyond.

>Just my point. I know it is a thousand times bigger, in the same
>way as I know that galaxies are thousands of times as far apart as
>the suns within them. But it is cognitively meaningless - a
>spurious precision.                kolin

True, unless you happen to be working in tha field, and then the
difference between a Megaparsec and a Gigaparsec becomes crucial.

Chris Handley                                     chandley@otago.ac.nz
Dept of Computer Science                       Ph     (+64) 3-479-8499
University of Otago                           Fax     (+64) 3-479-8577
Dunedin, NZ