This rare vintage Minerva Bi-Compax Chronograph houses the legendary Calibre 13-20, a movement of enormous historical significance. First introduced in 1923 in collaboration with Dubois-Depraz, this was one of the earliest dedicated wristwatch chronograph movements. While originally a mono-pusher design, it evolved into the dual pusher format seen here by the early 1940s, offered in both 30- and 45-minute variants. The Minerva Cal. 13-20 was used in elite timepieces like the Panerai Mare Nostrum and Ferrari Chronographs. As Minerva transitioned under Richemont ownership, this calibre—and the machines that produced it—became central to Montblanc’s Minerva revival in high horology.

The Cal. 13-20 is a masterclass in mid-century Swiss chronograph engineering and its architecture is defined by:

• A column wheel chronograph mechanism, highly prized for smooth engagement.
• Hand-finished details: beveled edges, polished components, and Geneva striping on plates and bridges.
• A screwed balance, Breguet hairspring, and solid steel return springs—hallmarks of high-grade chronometers from the era.
• Notably, the minute wheel bridge and set lever spring are combined—an uncommon feature that showcases movement minimalism and manufacturing precision.

The movement bears the original Minerva “arrow in circle” hallmark on the train side, along with the RFV (Registered Design) stamp—authenticating its originality. 

Dial Scales & Their Purpose

• Tachymeter (outer scale):
  Measures speed over a fixed distance (e.g. km or mile).
  Used by pilots and drivers to calculate travel speed.
• Pulsometer (middle scale):
  Calculates heart rate based on 30 beats.
  Designed for medical professionals—doctors, field medics.
• Telemeter (inner spiral scale):
  Measures distance to an event using sound delay (e.g. lightning/thunder or artillery).
  Used by military personnel to estimate shelling or storm distance.

Bi-Compax Subdials:

• Left: Running seconds
• Right: 30-minute counter for chronograph timing

Every element—Arabic numerals, subdial calibrations, two-tone dial and the minute track—remains crisp and original, untouched by restoration.

The 33 mm stainless steel case, with a slim bezel and slightly domed acrylic crystal, is enhanced by stepped architecture and rare shrouded lugs—a feature also seen in iconic IWC Da Vinci. These lugs were both functional (protecting spring bars) and stylistic, now a sought-after trait among serious vintage collectors.

• Case material: Stainless Steel
• Case size: 33 mm (without crown)
• Lugs to lugs: 42 mm
• Thickness: 12,5 mm1
• Movement: Cal. 13-20
• Swiss Made