From: [email-masked] (Jonathan McDowell)
Date: Thu, 22 Apr 93 15:32:42 -0400

Clive (and everyone else) -

I got this from John Roberts ([email-masked]):

CIPM, 1990   [Comite International des Poids et Mesures]

DRAFT RESOLUTION D TO THE 19th CGPM

The 19th Conference Generale des Poids et Mesures,

*decides* to add to the list of SI prefixes to be used for multiples and
submultiples of units, adopted by the 11th Conference Generale des Poids
et Mesures (CGPM), Resolution 12, paragraph 3, the 12th CGPM, Resolution 8,
and the 15th CGPM, Resolution 10, the following prefixes:

Multiplying factor       Prefix   Symbol
    10^(21)              zetta    Z
    10^(-21)             zepto    z
    10^(24)              yotta    Y
    10^(-24)             yocto    y

[Footnote:]
The names zepto and zetta are derived from septo suggesting the number
seven (the seventh power of 10^3) and the letter "z" is substituted for
the letter "s" to avoid the duplicate use of the letter "s" as a symbol.

The names yocto and yotta are derived from octo, suggesting the number
eight (the eighth power of 10^3); the letter "y" is added to avoid the use 
of the letter "o" as a symbol because it may be confused with the number
zero.

----------

So this makes the full list:

!       y       -24     yocto
!       z       -21     zepto
!       a       -18     atto
!       f       -15     femto
!       p       -12     pico
!       n       -9      nano
!       u       -6      micro (Greek Mu)
!       m       -3      milli
!               0
!       k       3       kilo
!       M       6       Mega
!       G       9       Giga
!       T       12      Tera
!       P       15      Peta
!       E       18      Eka
!       Z       21      Zetta
!       Y       24      Yotta

!       c       -2      centi
!       d       -1      deci
!       D        1      Deka
!       h        2      hecto

  - Jonathan