> Gerhard Fiedler wrote:
>> suggest something like (uA/A), which adds some
>> information that ppm doesn't have. And the specific problem with ppb i=
s
>> that "billion" is quite an ambiguous expression.
>=20
> HUH? million=3D1E6, billion=3D1E9, trillion=3D1E12,
> gazillion1E12E12 <G>? dollars of US debt.
> What is ambiguous about billion?=20

My text in the message from which you cited started with "The NIST sugges=
ts
...".

I have posted that link before, and Russell just posted it again... good
reading, and it includes the reason for their suggestion:=20

"In keeping with Ref. [6: ISO 31-0], this Guide takes the position that t=
he
language-dependent terms part per million, part per billion, and part per
trillion, and their respective abbreviations "ppm," "ppb," and "ppt" (and
similar terms and abbreviations), are not acceptable for use with the SI =
to
express the values of quantities. Forms such as those given in the
following examples should be used instead.

"Examples: a stability of 0.5 (=B5A/A)/min  but not: a stability of 0.5
ppm/min
...

"Because the names of numbers 10^9 and larger are not uniform worldwide, =
it
is best that they be avoided entirely (in most countries, 1 billion =3D 1=
 =D7
10^12, not 1 =D7 10^9 as in the United States); the preferred way of
expressing large numbers is to use powers of 10. This ambiguity in the
names of numbers is one of the reasons why the use of ppm, ppb, ppt, and
the like is deprecated. ..."

(from http://physics.nist.gov/Pubs/SP811/contents.html).

> Or do other countries have a different value?

Yes. Even though it seems that Britain has recently adopted the use of
"billion" for both 10^9 and 10^12 (which doesn't really diminish the
ambiguity :), many other (also non-English speaking) countries have
expressions similar to "billion" that mean 10^12 there.=20

Gerhard

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