In the mid-1950s, Rolex was on the verge of transforming its watch suite with something truly groundbreaking: a movement that could not only keep time with exceptional precision, but also display both the day of the week and the date in full. That moment marked the dawn of the Rolex Day-Date, and at the heart of that moment was the Caliber 1055and its refined iteration, Caliber 1055B.
While Rolex would later perfect its calendar mechanisms with instant date and day jumps, the 1055B stands today as a cornerstone of Rolex’s calendar movement lineage — a bridge between early automatic chronometers and the modern President era.
Technical Specifications
| Feature | Specification |
|---|---|
| Movement Type | Automatic self-winding |
| Base | Rolex Caliber 1055 |
| Reference | 1055B |
| Diameter | ~28.50 mm |
| Height | ~7.10 mm |
| Jewels | 25 |
| Frequency | 18,000 vph (2.5 Hz) |
| Functions | Hours, minutes, central seconds; day & date displays |
| Chronometer Certified | Yes |
| Production Era | Mid-1950s (≈1957 onward) |
This evolution of the original 1055 introduced small but meaningful refinements — notably a slightly greater height (7.1 mm vs. 7.0 mm) and changes in the dial plate and balance architecture aimed at greater robustness and accuracy.
Historical Context & Development
Birth of the Day-Date
Rolex introduced the Day-Date line in the late 1950s, at a time when calendar watches were becoming increasingly desirable among collectors and professionals alike. The original Caliber 1055 was groundbreaking for its dual calendar display, and the 1055B built on that platform with thoughtful refinements that enhanced reliability and performance.
Unlike future Rolex calendar calibers that pushed for instantaneous day and date changes, the 1055B’s displays changed over a broader transition at midnight — typical for the era but distinct from later Rolex standards. It nevertheless carried the coveted Chronometer certification, a testament to its meticulous timekeeping.
Movement Architecture & Features
While specific internal diagrams are scarce, the 1055B embodies the robust architecture Rolex was perfecting in the 1950s:
Automatic Winding & Escapement
- Bi-directional rotor winding system — a hallmark of Rolex’s automatic calibers.
- Traditional Swiss lever escapement for reliable regulation at 18,000 vibrations per hour.
Calendar Mechanism
The integrated day and date displays were mechanically linked and locally advanced via the crown — a significant engineering achievement at the time.
Chronometer Regulation
COSC certification ensured Rolex could mark these watches with Superlative Chronometer Officially Certified on the dial — an early nod to precision standards that would become a hallmark of the brand.
Watches That Feature Caliber 1055B
The 1055B movement was fitted primarily in early iterations of the iconic Rolex Day-Date, with references including:
- Rolex Day-Date 6611 & 6611B — One of the most collectible vintage Day-Dates, often seen in precious metal cases with early Rolex dial printing.
- Rolex Day-Date 6612B — Another early Day-Date variant powered by the 1055B movement, with collectors valuing its period aesthetics and mechanics.
These watches, especially in original condition with gilt or early printed dials, remain highly prized among vintage Rolex enthusiasts precisely because of the historical importance of the movement inside.
Why 1055B Matters to Collectors
Collectors love the 1055B for several reasons:
1. Historical Significance
It sat at the dawn of Rolex’s Day-Date lineage — the movement that helped birth what would become one of the brand’s most iconic models.
2. Rarity
Because production spans were short and relatively few units were made compared to later Rolex calibers, watches with 1055B are inherently rarer than many contemporaries.
3. Mechanical Charm
The classic feel of its calendar transitions, balance design, and period-correct finishing give it a distinctive vintage mechanical personality appreciated by purists.
Conclusion
While not as technologically evolved as later Rolex calibers with instantaneous calendar changes, the Caliber 1055Bholds a special place in the Rolex canon. It represents a transitional yet pivotal moment — when Rolex refined its automatic chronometer expertise and charted a course for one of its most enduring lines, the Day-Date.
Whether you’re drawn to vintage mechanics, historical milestones, or simply the story behind Rolex’s horological evolution, the 1055B stands as a compelling chapter in the story of one of watchmaking’s most celebrated brands.
