Unique six-character alphanumeric code permanently identifying a serial publication, such as a journal or magazine, or a non-serial publication, such as a dissertation or thesis. Examples are JECLB3 as the Coden for the ‘Journal Of Economic Literature,’ LANCAO for the journal ‘Lancet,’ and NATUAS for the journal ‘Nature.’ The first four characters of a Coden are always letters as a mnemonic for the publication, the fifth is a distinction character, being a letter from A to F, and the sixth is a letter from A to Z or a number from 0 to 9, being a computed check-character that helps in identifying typographical mistakes in the code. This coding covers publications in all subject areas even though it was developed by the American Society For Testing & Materials (ASTM), and processed by the Chemical Abstracts Service (CAS).