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Re: syntax for expressing millibar (fwd)

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  • Subject: Re: syntax for expressing millibar (fwd)
  • Date: Wed, 28 May 2003 16:46:53 -0600
------- Forwarded Message

Date:    Wed, 28 May 2003 16:45:46 -0600
From:    Russ Rew <address@hidden>
To:      Janine Goldstein <address@hidden>
Subject: Re: syntax for expressing millibar 

Janine,

> Is this documented somewhere?  I hate to bug you every time I come across
> a unit that I do not see on the UDUNITS Supported Units page.

Yes, the acceptable prefixes are documented near the end of the
reference documentation, which you get to by following the "C manual
page" or "FORTRAN manual page" links on the udunits home page:

  http://www.unidata.ucar.edu/packages/udunits/

How you use the udunits utility program is documented in the reference
documentation for that program, which you get to by following the
"utility manual page" link on the udunits home page.

The fact that "bar" is an acceptable unit of pressure is documented
under the "PRESSURE OR STRESS" heading of the supported units table,
which you can get to by following the "Supported Units" link on the
udunits home page, along with other units of pressure such as 
"standard_atmosphere".  "pascal" is also defined elsewhere in the same
file, which I just happened to know could also be a unit of pressure.

The fact that you can just use prefixes directly with units, such as
"m" with "bar" to get "mbar" is documented as part of the
documentation for the utScan() function in the C or Fortran reference
documentation, where it says:

  utScan() understands most conventional prefixes and abbreviations:

  ...

but is probably more easily seen in the examples like "cm" for
"centimeters".

It would be useful if there were a web page on which you could just
type in a candidate units specification, such as "m_bar" and it would
return either the canonical form indicating that unit specification
was correct or else an error message indicating it didn't recognize
the unit.  But currently I don't know of such a web page, so you have
to get the "udunits" utility program for that purpose.  Providing the
web service would be a good web programming exercise, so maybe we'll
have one of our students do it ...

--Russ

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