Re: NetCDF Digest - Vol 1 : Issue 278

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: Re: NetCDF Digest - Vol 1 : Issue 278
• From: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Date: Thu, 03 Aug 1995 09:50:13 -0600

Harvey,

>Date: Thu, 3 Aug 1995 20:14:11 +1000 (EST) 
>From: Harvey DAVIES <hld@xxxxxxxxxxxx>
>To: netcdfgroup@xxxxxxxxxxxxxxxx
>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@xxxxxxxxxxxxxxxx>