[time-nuts] unités & conventions internationales

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Mon Oct 12 15:16:39 UTC 2009

On 10/12/09 2:25 AM, "AL1" <alain2.bouchet at wanadoo.fr> 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!
Indeed.. Possibly, though, it was the (almost) universal use of SI that led
to the problem with the data.  It probably never occurred to the people at
JPL that someone would use anything other than SI units, and so they didn't
check.  The numbers, in either units set (pounds or Newtons) were very small
compared to other things going on, so the discrepancy between observations
(noisy) and the model outputs (also noisy) as the result of a factor of 5
error in magnitude to the inputs to the modeling code was attributed to
other things.

(I work at JPL, but I haven't talked to the navigators for the ill-fated '98
missions, so I don't know.. Just speculating here)

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