<p class="font_8">**Zenith Chronomaster El Primero Full Open Skeleton Model 03.2153.400/78.C813 Review by A.I. WatchMetrics**

### Watch Summary:
The Zenith Chronomaster El Primero Full Open Skeleton is a striking example of a sport/active watch with a bold design and technical prowess. This model is part of Zenith's renowned El Primero line, known for its high-frequency chronograph movements. The open-worked dial showcases the intricate mechanics of the El Primero 400B automatic movement, which boasts a 50-hour power reserve. This watch is ideal for enthusiasts who appreciate horological craftsmanship and a sporty aesthetic. Its skeletonized design and chronograph functionality make it a standout piece for those who value both style and precision.

### Overall Watch Rating: 8.1/10.0

- **Functions Metric (9.0/10.0)**
- The watch features a chronograph function, high water resistance suitable for active use, and a transparent caseback that enhances its appeal. The lume on the hands and indices ensures readability in low-light conditions.

- **Movement Metric (8.8/10.0)**
- The El Primero 400B automatic movement is a hallmark of Zenith's innovation, offering a high-frequency chronograph with a 50-hour power reserve. Its precision and historical significance contribute to a strong movement score.

- **Dials &amp; Design Metric (8.5/10.0)**
- The skeletonized dial is a testament to Zenith's craftsmanship, allowing a view of the movement's complexity. The design is both innovative and aesthetically pleasing, though it may not appeal to those preferring traditional dials.

- **History &amp; Innovation Metric (8.4/10.0)**
- Zenith's El Primero line is historically significant, being one of the first automatic chronographs. This model continues the legacy with modern design elements and technical advancements.

- **Material Metric (8.2/10.0)**
- The use of high-quality stainless steel and sapphire crystal ensures durability and a premium feel. The finishing is excellent, though the materials are standard for this price range.

- **Versatility Metric (8.0/10.0)**
- While primarily a sport watch, its design allows for some versatility in casual settings. However, it may not suit formal occasions due to its bold aesthetic.

- **Complications Metric (7.8/10.0)**
- The chronograph is the primary complication, well-executed and integral to the watch's identity. The lack of additional complications limits the score slightly.

- **Rarity Metric (7.5/10.0)**
- While not a limited edition, the El Primero's reputation and the skeleton design add a degree of exclusivity. Production numbers are moderate, maintaining some rarity.

- **Brand Metric (7.0/10.0)**
- Zenith is a respected brand with a strong heritage in chronograph movements. However, it lacks the widespread recognition of some luxury peers, affecting its brand score.

### Celebrity and Historical Figures:
- **LeBron James** – NBA star, known for wearing Zenith watches, including the El Primero line, during public appearances.
- **Russell Westbrook** – Another notable NBA player who has been seen wearing Zenith watches, highlighting the brand's appeal among athletes.</p>