Omega Caliber 2403A: A Refined Chapter in Manual Co-Axial Innovation

The Omega Caliber 2403A is a refined version of the original Caliber 2403, one of the first manual-wind movements to incorporate Omega’s revolutionary Co-Axial escapement. Introduced in the early 2000s, this movement combined traditional horological elegance with a pioneering mechanism developed by master watchmaker George Daniels. The 2403A version reflects Omega’s iterative improvement process, focusing on technical stability and manufacturing consistency.

While not widely known among casual collectors, the 2403A holds an important place in Omega’s transition from outsourced movements to fully re-engineered, in-house calibers that support the brand’s long-term pursuit of precision, longevity, and innovation.

Technical Specifications

• Type: Manual-winding

• Base Caliber: Modified ETA 7001 / Peseux

• Jewels: 17

• Diameter: 23.3 mm

• Height: 2.5 mm

• Frequency: 25,200 A/h (3.5 Hz)

• Power Reserve: ~48 hours

• Functions: Hours, minutes, small seconds

• Chronometer Certified: Yes (COSC)

• Escapement: Co-Axial (Omega-modified Daniels design)

At its core, the Caliber 2403A remains a compact, thin, manual-wind movement, well-suited for elegant dress watches. The "A" revision brought minor improvements to the Co-Axial system's reliability, balance wheel performance, and fine-tuning tolerances.

Evolution from the Original 2403

While visually and dimensionally similar to the base 2403, the 2403A featured internal adjustments that improved the consistency of rate results, especially during the chronometer certification process. These refinements helped Omega ensure greater long-term durability and smoother production as Co-Axial technology scaled across the lineup.

The Co-Axial escapement itself remained untouched in its overall architecture: a three-level system that dramatically reduces sliding friction compared to the traditional Swiss lever escapement. The result is better long-term rate stability, reduced need for lubrication, and extended service intervals.

Movement Finishing

Omega didn’t cut corners on aesthetics. The 2403A was beautifully finished with:

• Geneva stripes on the bridges

• Rhodium plating

• Polished screw heads

• Anglage (beveled edges)

• Signed Omega Co-Axial engravings

These decorative flourishes were visible through sapphire casebacks in many models, reflecting Omega’s renewed dedication to haute horlogerie standards in the modern era.

Watches That Featured the 2403A

The Caliber 2403A was most commonly used in De Ville Co-Axial Chronometer models—timepieces that embraced classical case proportions and understated elegance. Case materials included stainless steel, yellow gold, and red gold, with sizes typically around 38–41mm, depending on the design.

Watch designs were focused on purity:

• Two or three-hand displays

• Small seconds at 6 o’clock

• Domed dials with applied indices

• Minimalist Co-Axial Chronometer text

These watches were aimed at enthusiasts who appreciated manual-wind interaction, technical innovation, and a low-profile wrist presence.

Collectibility and Significance

Omega’s manual Co-Axial movements like the 2403A are relatively rare in the modern market. As most contemporary buyers favor automatics, Omega produced only a limited number of manual-wind Co-Axial models before transitioning to larger, fully in-house calibers such as the 8400 series.

Collectors value the 2403A for:

• Its niche appeal

• First-generation Co-Axial mechanics in manual form

• Slim, chronometer-certified construction

• Refined finishing rarely seen in entry-level luxury watches

These pieces have become harder to find, and well-preserved models with box and papers are especially desirable for collectors of modern Omega rarities.

Final Thoughts

The Omega Caliber 2403A represents a quiet triumph in Omega’s Co-Axial journey. It’s not only a technical refinement of the groundbreaking 2403 but also a symbol of Omega’s intent to blend tradition with innovation in new and meaningful ways. As one of the few manual Co-Axial movements ever made, it stands out as a rare offering for connoisseurs who enjoy winding their watch and knowing there’s horological significance ticking underneath.

For those who admire George Daniels’ legacy, Omega’s modern resurgence, and understated excellence, the 2403A is a true mechanical gem.