A recent social media discussion asked about the purpose of subfield $m of the MARC 082 field, the field for DDC numbers in the bibliographic format. Subfield $m is a simple binary subfield, in which you can enter a value of a to mark the number as standard or b to mark it as optional.
If you don’t use this subfield, you’re not alone. In a perfect world, it would probably be nice to always have this information specified. But in practice, I think it’s safe to say catalogers are mostly entering standard numbers into the 082 field.
Please do use subfield $m if you’re recording an optional number (so specifically, $m b). If you really want to be thorough, you can use it for standard numbers as well.
Until recently, subfield $m was marked as mandatory on the 082 page in OCLC’s Bibliographic Formats and Standards documentation. We’ve changed that to mark it as optional. If you’re curious, it was probably marked mandatory because it’s marked that way in the Library of Congress’s National Level Requirements. I tip my hat to my OCLC colleague Jay Weitz for tracking that down.
While we’re on the subject of MARC, I wanted to remind you of the changes earlier this year to subfield $2. In short, this subfield now carries date and language information in addition to edition, to give a fuller picture of the provenance of a DDC number. You may have seen examples of this in WorldCat, and as of this writing, the Library of Congress MARC documentation page still has the additions in red text.
If you use a macro or Connexion constant data for subfield $2, you might consider adding $m to it too.
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