Jaeger-LeCoultre uses numbers to identify their calibres. There is a rough system to their numbering, with smaller calibres getting lower numbers and larger and more expensive ones assigned higher numbers. Jaeger-LeCoultre also tends to use similar numbers for related calibres, though this isn't always the case. In most cases, variants of a base calibre in the same generation will have numbers in the same decade while major revisions will get a new decade. For example, Calibre 889 was replaced by Calibre 899, and variants of the latter included Calibres 896 and 898.
Numeric suffixes denote minor revisions, as is the case for other movement manufacturers. Some Jaeger-LeCoultre calibres have a “/2” variant, for example, when changes were made that did not require a new calibre number.
Suffix letters refer to complications or characteristics “SQ” refers to a skeleton (“squelette”), while other letters often indicate complications, certification, or applications. For example, Calibre K880G was a chronometer certified version of Calibre 880 with Kif shock protection.