Thanks Roy,

David, Ros: do you accept Roy's answer? If so, cf-python and the cf-checker 
should presumably be updated to flag "psu" as an invalid unit?

regards,
Martin

________________________________
From: Lowry, Roy K. [[email protected]]
Sent: 18 July 2017 14:00
To: Juckes, Martin (STFC,RAL,RALSP); [email protected]; 
[email protected]; [email protected]
Subject: Re: Is "psu" a valid cf unit?


Hello Martin,


This topic has been debated at length in CF. To cut a long story short, the 
term 'Practical Salinity Unit' was coined when the 1978 Practical Salinity 
scale was devised. However, the term fell out of favour with the physical 
oceanographic community whose current recommended practice is that Practical 
Salinity - a ratio - should be a dimensionless number.  CF followed this 
recommendation and so PSU is not a part of CF.


Have a dig around in the mailing list archive if you want to find out more.


Cheers, Roy.


Please note that I partially retired on 01/11/2015. I am now only working 7.5 
hours a week and can only guarantee e-mail response on Wednesdays, my day in 
the office. All vocabulary queries should be sent to [email protected]. 
Please also use this e-mail if your requirement is urgent.


________________________________
From: CF-metadata <[email protected]> on behalf of 
[email protected] <[email protected]>
Sent: 18 July 2017 13:43
To: [email protected]; [email protected]; 
[email protected]
Subject: [CF-metadata] Is "psu" a valid cf unit?

Hello David, all,

Is "psu" a valus CF unit? It is not in Udunits, but it is added in cf-python as 
a unit alias and also appears to be accpeted by the cf-checker. I can't see any 
mention of it in the CF Convention document: the latter only lists level, 
layer, and sigma_level permitted departures from Udunits,

regards,
Martin

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