XR Cross Reference (WPI No.)

1999-3856835 in xr

90-3348418 in xr

The Derwent WPI (World Patent Index) Accession Number and the WPI Week Number are cross-referenced in the XR field. The formats will contain either a two-digit (YY-NNNNNN/WW) or four-digit (YYYY-NNNNNN/WW) year depending on the accession number of the record it references. Records added to the database from September, 1999 forward contain the complete four-digit accession year; records added prior to that date contain only the last two digits of the accession year.

In both formats, WW indicates the Derwent Week Number. Search as in the example above.