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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 referencemanual I kept track on difference between version 0 and 2 and I believethose 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 Telex: 847908 ECMWF G E-mail: milan.dragosavac@xxxxxxxxx