>Date: Thu, 3 Aug 1995 20:14:11 +1000 (EST)
>From: Harvey DAVIES <hld@dar.csiro.au>
>To: netcdfgroup@unidata.ucar.edu
>Subject: Re: NetCDF Digest - Vol 1 : Issue 278
In the above message you wrote:
> > > billion P 1.0e9
> > > trillion P 1.0e12
> >
> > Don't the British use `billion' to mean 1.0e12 (i.e. isn't the
British
> > `billion' the USA's `trillion')?
>
> The old British billion & trillion were more logical -- 1st 2 letters
(bi or
> tri) represented the power of million, giving 1e12 & 1e18. In Australia
the
> meanings have clearly changed (over the last 20 years or so) from these
to the
> USA usage. I seem to remember a news item a year or so ago to the effect
that
> the British had officially adopted (I can't remember how) the USA billion
(& I
> guess trillion). Perhaps some UK reader would like to clarify this.
I'll postpone adding these until I hear something more definitive,
preferably by one of our UK cousins.
I've added `sidereal_month' and `tropical_month'.
I've tentatively decided on the following for some other time units:
common_year P 365 day # exact
leap_year P 366 day # exact
Julian_year P 365.25 day # exact
mean_year P 365.2425 day # exact
year P mean_year
month P year/12 # on average
NOTE: The previous definition of `year' was
year P 3.153600e7 second # exact
which, as you noted, was exactly 365 days. I decided to define it
as an alias for `mean_year' because I believe that that will be the
most common usage (anyone dealing in years will typically include many
leap-years). This will mean, however, that extant netCDF datasets
that use the unit `year' rather than a more unambigous unit (e.g. 365
days) will either be off in time by about 0.00066 ((mean_year -
common_year)/common_year) or that the unit specification will have to be
replaced with `common_year'.
Please tell me what you think.
--------
Steve Emmerson <steve@unidata.ucar.edu>