Omega Speedmaster Mark 4.5 ref. 176.0012

Affectionately nicknamed the Mark 4.5 by collectors, the Omega Speedmaster reference 176.0012 occupies a fascinating place within the experimental lineage of the Omega Speedmaster “Mark” series. Developed during a period when Omega sought to recoup research and development costs following the cancellation of the Alaska Project, the Mark series incorporated several of the project’s specifications and innovations, introducing bold tonneau-shaped cases and integrated tachymeter bezels that departed from the traditional Moonwatch aesthetic. Although never officially designated as part of the Mark family, the unofficial “Mark 4.5” combines the distinctive case architecture of the Omega Speedmaster Mark IV with the robust automatic chronograph movement later used in the Omega Speedmaster Mark V. At its heart is the Omega caliber 1045, which is based on the legendary Lemania 5100 — a famous workhorse movement known for its central chronograph minutes, day-date display, and 24-hour indicator.

This watch is in fair to good overall condition, showing noticeable signs of regular wear including scratches, scuffs, and dents. Both the case and bracelet have been refinished in the past to varying degrees. There are some imperfections in the refinishing, including slight overlap between the brushed and polished surfaces on certain areas of the case, as well as some misalignment in the bracelet brushing, though these are primarily noticeable only upon very close inspection. In addition to surface wear, the bracelet shows moderate stretch consistent with regular use. Some corrosion is present between the lugs on the case. The crystal shows scratches and scuffs, and age-related wear is visible beneath the crystal, including small specks, dust, and grime present on the dial and hands.

The movement is currently running properly with all functions operating as intended, though its service history is unknown. The crown exhibits a slight resistance when the hands are manually advanced past midnight during the date change; however, this does not affect the quickset function or the normal operation of the date change. The watch produces a slight rattling sound when gently shaken, likely from the winding rotor, though this does not affect its operation or winding. Measured on a timegrapher in a neutral position, this watch recorded approximately +45 seconds per day with amplitude around 220 degrees and a beat error of 0.1ms. We recommend a service at the buyer’s expense for optimal accuracy and long-term reliability.

Additional photos and timegrapher results are available on request.

This watch does not come with its original box or papers.

Brand: Omega

Model: Speedmaster (Mark 4.5)

Reference: 176.0012

Year: 1984

Serial number: 4554XXXX

Case size: 42mm

Lug-to-lug: 45mm

Case thickness: 15.4mm

Case material: Stainless steel

Dial color: Black

Movement: Omega caliber 1045, base movement Lemania 5100

Complications: Chronograph, date, day, 24-hour (day/night) indicator

Water resistance: 50 meters (vintage watches should not be considered water resistant until pressure tested)

Strap/bracelet: Original stainless steel bracelet with clasp marked “1162” and endlinks marked “172”

Wrist size: 19.5cm

Lug width: 22mm