[time-nuts] unités & conventions internationa les

[Arnold Tibus]

On Mon, 12 Oct 2009 11:25:48 +0200, AL1 wrote:

>HI all timenuts lovers,

>i think it is not a question in our hobby : we have to use the international unities system  (SI) as result fron the international conventions.
>I warm recommand to read that:
>http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf

>it is on the site of Bureau International des poids et mesures (BIPM), and is of first interest.
>Naturally in our life we can do as we think (...!?), but in any scientific domain it is no question of approximative!
>remember the lost of Mars orbiter due at the misusing of unities!

>Meilleures salutations à tous
>Alain Bouchet
>ingénieur en métrologie


Merci beaucoup Alain, 

I didn't have this document in hand, but I tried always to follow the known 
standards thus avoiding possible misinterpretations. My concern here was 
specially the problem with the different understandings of 'billion' and 'trillion',
therfore addressing my question to Mark as originator of the very helpful program 
'Lady Heather'.

I see now that this was tackled already internationally by the BIPM 
Standardization Organisation. 

Magnus, I do underline everything you said, as well the statement
"This can only be solved by means of education and correction."
But that the 'µ' sign (and other greek characters used and wrtten in books 
for math. and physical faculties sind centuries) could not yet find the way into 
modern computers is not at all understandable nor acceptable.

Concerning the 'ppm'- problem I quote from am. document:

"The term 
ppm
, meaning 10^-6 relative value, or 1 in 10^6, or parts per million, is 
also used. This is analogous to the meaning of percent as parts per hundred. The 
terms 
parts per billion
, and 
parts per trillion
, and their respective abbreviations 
ppb
,
and 
ppt
, are also used, but their meanings are language dependent. For this reason
the terms ppb and ppt are best avoided. (In English-speaking countries, a billion is
now generally taken to be 109 and a trillion to be 1012; however, a billion may still
sometimes be interpreted as 1012 and a trillion as 1018. The abbreviation ppt is also
sometimes read as parts per thousand, adding further confusion.)

When any of the terms %, ppm, etc., are used it is important to state the
dimensionless quantity whose value is being specified."

Sounds understandable, so there is nothing to be added from my side.
Hopefully we do in future not experience more of such 'Mars Orbiter disasters', 
this was not the only one, it is just the peak of a big pyramide of comparable 
'accidents'.

many thanks as well to the other commentators

Arnold