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[UDUNITS #AQJ-619467]: UDUNITS - unit multiplier

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  • Subject: [UDUNITS #AQJ-619467]: UDUNITS - unit multiplier
  • Date: Wed, 23 Aug 2006 12:32:17 -0600
Stuart,

> How do you set UDUnits and values for "250 millions years ago" and
> "13500 years before present" without it being interpreted as
> 250 million years before 11:45:36.098 AM MST August 23 2006?
> 
> Geological times in the Permian to the nearest second makes no sense.
> 
> "years since 1900-1-1" with integer times seems to work but
> "megayears before 00-1-1" does not.

My considered opinion on the matter is that one shouldn't expect a mere
units package to handle things like this.  If the physical quantity
in question is something like "millions of years before the present",
then the relevant unit should simply be "1e6 years" or "megayears"
and it should be up to the subsystem that handles physical quantities
in the scientific package in question to make sense of it.

I believe this is also in accord with NIST and ISO recommendations regarding
units: they shouldn't have attached metadata (see sections 7.4 and 7.5
of <http://physics.nist.gov/Pubs/SP811/sec07.html>)

Having said all that, you *might* be able to get away with a "unit" like
"-1e6 years since 1-1-1".  If so, then consider it a gift.  :-)

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: AQJ-619467
Department: Support UDUNITS
Priority: Normal
Status: Closed