Code names consist of 2 to 6 characters and follow certain loose conventions. In general, the broader a concept, the shorter the name of the series that represents it.
Longer names indicate components of a larger group.
No code name is longer than 6 characters. The first letter of a code name generally refers to the chapter that lists the series. A key to first letters in code names appears on page v of this section. Second Letters and Subsequent Letters Other guidelines, which refer to second letters, standard industrial classification numbers, BLS codes, and other considerations, are less strictly adhered to. The letter X may indicate a ratio or percentage change, or it may indicate a group excluding certain items.