The Zenith Chronomaster XXT Open Grande Date (Reference 03.1260.4039/21.C505) is a prominent, mechanically complex luxury timepiece originating from the bold design era of the mid-2000s under former Zenith CEO Terry Nataf. Famous for its partial skeletonization and high-frequency performance, it offers a "tourbillon-like" visual entertainment at a fraction of the cost.

• Case Size & Dimensions: It features a bold 45mm diameter stainless steel case, with a thickness of roughly 16.5mm and a lug-to-lug span of 53.5mm. 

• The Movement: Powered by the legendary in-house Zenith El Primero Caliber 4039. This automatic integrated column-wheel chronograph beats at a high-frequency of 36,000 vibrations per hour (10 beats per second), providing an ultra-smooth sweeping chronograph hand. 

• Power Reserve: Equipped with a 50 to 55-hour power reserve, monitored via a dedicated sector scale indicator located on the lower half of the dial.

• Open-Heart Cutaway: Positioned between the 8 and 12 o'clock marks, a meticulously framed dial window exposes the beating escapement, balance wheel, and a unique tri-spoke constant small seconds pinion.

• Grande Date (Big Date): Located near the upper right quadrant, this complication utilizes a dual-disk system. Expert reviewers highlight the mechanism's dual sapphire disk overlays as a highly entertaining and distinct mechanical layout.

• Dial Styling: Features a striking black Guilloche-textured dial adorned with elegant, radially arrayed blackened or silver-tone applied Roman numeral markers.

• Strap & Hardware: Outfitted on a premium 22mm black alligator leather strap pairing with a polished stainless steel double-deployment folding clasp.