UNITAS 6497 & 6498 vs Sea-Gull ST3600 & ST3620 | Complete History
From Swiss pocket watches to modern mechanical icons.
The UNITAS 6497 and 6498 are among the most influential hand-wound movement architectures in modern watchmaking. Originally designed for pocket watches, they later became a reference for large mechanical wristwatches and inspired modern calibers such as the Sea-Gull ST3600 and ST3620.
The Origins
The story begins in Switzerland, where UNITAS developed a family of large hand-wound movements intended for pocket watches. Two versions became particularly important: the 6497 and the 6498.
The 6497 follows the traditional Lépine pocket-watch layout, while the 6498 follows the Savonnette configuration. When adapted to wristwatches, this difference results in the characteristic 9 o'clock versus 6 o'clock small-seconds positions.
UNITAS / ETA 6497
Hand-wound movement with small seconds at 9 o'clock when adapted to a conventional wristwatch layout.
UNITAS / ETA 6498
Hand-wound movement with small seconds at 6 o'clock, often chosen for more classical dial layouts.
Why It Became a Classic
The architecture proved exceptionally successful thanks to its simplicity, reliability, serviceability and large dimensions. These characteristics made it ideal for oversized watches, display casebacks and skeletonized designs.
Over the decades, the movement family appeared in watches associated with names such as Panerai, Omega, Hamilton, Elgin, Waltham, Tissot, Arnex and Bulova, sometimes in standard form and sometimes as modified or decorated base movements.
When UNITAS became part of ETA, production continued under the names ETA/UNITAS 6497 and ETA/UNITAS 6498. Later versions such as the 6497-1, 6497-2 and 6498-1 preserved the original architecture while benefiting from modern manufacturing improvements.
The Sea-Gull Interpretation
As demand for large hand-wound movements continued, Sea-Gull adopted the proven architecture and adapted it to modern production methods, creating the ST3600 and ST3620.
Sea-Gull ST3600
Inspired by the 6497 layout, with small seconds at approximately 9 o'clock. Its open architecture makes it especially suitable for skeleton watches.
Sea-Gull ST3620
Inspired by the 6498 layout, with small seconds at approximately 6 o'clock. Its more symmetrical layout is often preferred for traditional and classically styled wristwatches.
Calibre Culture
The ST3600 used in CHRONIS mechanical watches follows the classic architecture associated with the UNITAS / ETA 6497 family.
Originally conceived as a large hand-wound movement for pocket watches, the 6497 architecture later became appreciated in wristwatches for its size, visual clarity and robustness.
Its large bridges, visible gear train and hand-wound construction make it particularly suitable for skeleton designs, allowing the wearer to observe the interaction between the mainspring barrel, wheels, escapement and balance wheel.
Quick Comparison
| Feature | ST3600 | ST3620 |
|---|---|---|
| Historical inspiration | UNITAS / ETA 6497 | UNITAS / ETA 6498 |
| Winding | Manual | Manual |
| Diameter | 36.6 mm | 36.6 mm |
| Beat rate | 21,600 vph | 21,600 vph |
| Power reserve | ~40 hours | ~40 hours |
| Small seconds | 9 o'clock | 6 o'clock |
The CHRONIS Perspective
At CHRONIS, we appreciate movements that are visible, understandable and emotionally engaging.
The ST3600 and ST3620 preserve the spirit of one of the most respected hand-wound architectures ever created: large, mechanical, reliable and full of character.
Because some movements do more than measure time. They tell a story.