The Hamilton H-21 is based on the Valjoux 7750. The H-31 is similar though based on the 7753. These movements most notable change compared to the standard version is the 60 hour power reserve.
The following elements have been modified:
- The entire kinematic chain has been refined, from the barrel to the escapement
- The escapement regulator has been suppressed, facilitating optimal reliability and precision
- The main spring has been improved to increase a typical power reserve of 60 hours.
- The mono-block rotor is distinctively skeletonized with an “H” shape and aviation-inspired cut-outs, a signature of individualization.