Glossary
An identifying number stamped on the case itself, which on some brands is issued separately from the movement number and the serial number.
On watches like Patek Philippe, the case and movement carry independent numbers that should both be checked and, where records exist, verified against the maker's own archive rather than assumed to match automatically. A case number that doesn't correspond to the movement number it's paired with can indicate parts from two different watches have been combined into one.
Browse the full glossary, or look up a serial number in the registry.