What does “Caliber” mean?

The caliber (also spelt caliber, or abbreviated cal.) is the brand's reference number for a watch movement. It identifies the movement's design and functions: for example, Rolex caliber 3235 powers the current Submariner Date and Datejust 41, caliber 4131 the latest Daytona, and Omega's caliber 3861 the current Speedmaster Professional. 'Caliber' is also used loosely to mean the movement itself.

The caliber matters for identifying generations, understanding features such as power reserve and accuracy, and planning service. Two watches that look identical can have different calibers from different production years, which affects value and how they are serviced. Dealers also check that the caliber is correct for the reference, since a swapped or incorrect movement is a serious originality problem, especially in vintage watches.

Example: 'Caliber 3235, 70-hour power reserve, last serviced in 2023.'