Cal. JB4-24h is a round 14 ligne chronograph movement produced by Excelsior Park in the 1940s and 1950s. It is a hand-winding movement with 30 or 45 minute counters at 3:00 on the dial. It features two unusual features not found on many other chronographs at the time:
- A central 24 hour hand is connected to the running time. This is said to be an aid in orienteering: The instructions call for orienting the standard hour hand with the sun, which results in the small hand marked with “N” pointing north.
- A second crown at 9:00 can be used to adjust the small seconds hand when pressed and rotated. This allows the time to be set precisely to a reference.
These functions appear to be paired in only one version of the movement, though they use different components and could have been delivered separately.
All Excelsior Park Cal. JB4 family movements are instantly recognizable thanks to the distinctive U-shaped cock that supports the chronograph wheels. Nearly every other chronograph uses a Y- or wishbone shaped cock or bridge. The overall design of the movement is also “reversed” from many other chronographs, with the rabbit-shaped hammer falling on the crown side and a counter-clockwise balance cock. Although not a finely-finished movement, it is high in specification with a Breguet spiral hairspring, screwed balance, and machined springs. The chronograph minutes recorder is equipped with a “sautoir” (jumping mechanism).
One version, Cal. JB4-24h includes two novel features: A central 24 hour hand used for orienteering and a “seconds corrector”, allowing manual adjustment of the running seconds hand using a crown at 9:00.
Excelsior Park chronograph movements were used by Gallet, Zenith, and Girard-Perregaux as well as in-house by Excelsior Park and Moeris. These were roughly similar apart from their finishing and the specification of a mobile stud carrier by some brands. The “JB” stands for Jeanneret-Brehm, the name of the founder of the Excelsior Park factory.
| Complications | Notes | |
|---|---|---|
| Cal. JB4 | Chronograph minute counter | Base movement |
| Cal. JB4-68 | Cal. 4 base | Movable hairspring stud |
| Cal. JB4-24h | Cal. 4 base; 45 minutes, 24 hour hand | |
| Cal. JB40 | Chronograph 45 minutes, 12 hours | |
| Cal. JB40-68 | Cal. 40 base | Movable hairspring stud |
| Cal. JB42 | Chronograph 45 minutes | Oval 12×13 ligne |