Re: [bufrtables] More on table versions

Hi Milan:

I see that in the BUFRDC tables, B0000000000098000000.TXT and 
B0000000000098002001.TXT, the 013015 bit width changed from 10 to 12, and 
apparently the scale also changed from 1 to 7:

version 0 (B0000000000098000000.TXT):
013015 SNOWFALL (AVERAGE RATE) M/S 1 0 10
and version 2 (B0000000000098002001.TXT):
013015 SNOWFALL (AVERAGE RATE) M/S 7 0 12
I see, as you mention, the change to SI units in version 2, which affects the 
scales.

So this is a pretty clear example of changes to scale,reference and/or bit 
width to operational descriptors. Without knowing these, any messages that use 
those descriptors will be incorrectly decoded.

So how do we know when "links are needed" to other tables? Does the WMO 
maintain canonical copies of previous table versions of the Table documents that we can 
double check? Should we use BUFRDC tables as canonical ?

Regards,
John

Milan Dragosavac wrote:
Dear John,

I think you can use the latest version 13 of the tables and make links to any other tables with smaller version number. In my Bufr reference
manual I kept track on difference between version 0 and 2 and I believe
those are the only differences. However, I am not sure if those differences refer only to Ecmwf's maintained tables or not. All entries are for table B class 13 where units were changed and consequently scales. The data width was changed only for 013015 snowfall (average rate) from 10 to 12.

To summarise, I think it is very safe to use version 13 and make links to any other when needed.

Best regards

Milan
Milan Dragosavac

ECMWF
Shinfield Park, Reading, Berkshire, RG2 9AX, UK

Tel: (+44 118) 949 9403
Fax: (+44 118) 986 9450
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E-mail: milan.dragosavac@xxxxxxxxx