@richardmille: The barrel serves as the watch's energy reservoir, much like the fuel tank of a racing car. As the mainspring is wound, either manually or by the rotor, it stores mechanical energy, which is then released progressively to the gear train. At Richard Mille, the barrel rotates faster than in a conventional watch, one revolution every 5 hours instead of 7.5. This reduces adhesion between the mainspring coils, ensuring a more stable delivery of energy throughout the power reserve, which ranges from approximately 40 hours to as much as 10 days, depending on the model. Some movements feature a double-barrel system that distributes the stored energy between two barrels rather than one. This lowers the load on the gear train, bearings and pivots, reducing friction, improving long-term reliability and enhancing torque stability for more consistent performance.