[Ferret] question about using proleptic gregorian calendar

[Ingo.Bethke@xxxxxxxxxxxxxx]

Hi,

We are planning to have some simulations which start 1400 and will cross the
udunits standard calendar discontinuity in 1582.  

As far as I experienced, ferret 5.8 doesn't accept the attribute value
'proleptic_gregorian' from the CF convention. However, the documentation says
that Ferret's gregorian calendar is proleptic gregorian but nc-files with the
attribute value 'gregorian' or 'standard' are identified as mixed julian/gregorian. 

So, how can I make ferret identify my calendar as proleptic?     

Thanks, 
Ingo Bethke