The Zenith El Primero Chronomaster Triple Calendar Moonphase 40mm (most notably Reference 01.0240.410 or 02.0240.410) is a legendary, highly complicated vintage timepiece introduced by Zenith in 1994 and produced until the early 2000s. It stands as one of the most mechanically complete expressions of the iconic El Primero high-frequency movement, merging a race-born chronograph with an elegant dress watch aesthetic.

• Case Size: 40mm diameter, approximately 13mm thickness, and a compact 46.5mm lug-to-lug measurement. It features distinctive broad, stepped fluted lugs and a triple-stepped bezel. 

• Movement: Zenith Caliber El Primero 410 automatic column-wheel chronograph. It operates at a high frequency of 36,000 vibrations per hour (5 Hz) and boasts a 50-hour power reserve.

• Complications: Full triple calendar (Day aperture at 10 o'clock, Month aperture at 2 o'clock, and Date window tucked between 4 and 5 o'clock) paired with a poetic Moonphase indicator integrated into the 12-hour sub-dial at 6 o'clock. 

• Dial Aesthetics: A stunning silver guilloché dial featuring applied Roman numeral hour markers, polished hands, and an outer tachymeter scale. 

• Certification: Most iterations from the 1990s are COSC Chronometer Certified, proudly marked with "Chronometer" on the dial text.