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In-house manufacture caliber
Medium-large: suits wrists 6.5 in+ (16.5 cm+)
42 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.
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Authentication
The 5 Hz El Primero beat rate must be confirmed through movement observation; tri-color sub-dial identity is the dial authentication.
Known issues in the market
- Cal. El Primero 400B is the heritage caliber; 36,000vph architecture distinguishes it from lower-beat alternatives.
- Tri-color sub-dial arrangement (silver, black, grey) is the El Primero identity marker.
| Area | What to check | What is correct | Red flag |
|---|---|---|---|
| dial | Tri-color sub-dial arrangement | Silver, black, and grey sub-registers in correct positions; El Primero tri-color identity intact | Mono-color sub-registers; incorrect color combination; dial substitution from another reference |
| movement | 5 Hz beat rate | Sweep seconds appears nearly continuous; 1/10th-second chronograph accuracy present | Stepping seconds visible indicating lower-beat substitution; 1/10th-second accuracy absent |
| caseback | Cal. 400B identity | El Primero 400B designation; column-wheel architecture; rotor finishing consistent with Zenith quality | Non-El-Primero caliber; cam-actuated architecture; incorrect caliber engraving |
Common legitimate replacements
- Original Chronomaster Original bracelet; leather strap an authorized factory option.
Expert resources: Zenith Chronomaster Original 03.2040.400 press materials. El Primero 400B caliber documentation.
Authentication guide
Last reviewed June 2026
The Chronomaster Original is the direct lineage successor to the original 1969 El Primero, with the tri-color dial and the Cal. 400B at 36,000bph. The original-format 38mm case is smaller than the Sport and the dial color zoning is the defining feature.
Sources: Zenith -- El Primero 400B history and Chronomaster Original documentation; Hodinkee -- El Primero 50th anniversary and Original reference; WatchUSeek -- Zenith Chronomaster authentication forum.




