Omega Caliber 9904 Watch Movement

Brand	Omega
Caliber Number	9904
Base Caliber	Omega 9300
Movement Type	Automatic, self-winding mechanical
In-House?	Yes
COSC?	Yes
METAS?	Yes
Jewels	54
Total Components	368 parts
Beat Rate	28,800 vph, 4Hz
Lift Angle	Unconfirmed
Power Reserve	60 hours
Barrel Count	2
Rotor Style	Ball-bearing
Hand-Windable?	Yes
Anti-Shock Device	Nivachoc
Escapement	Co-Axial
Balance Spring	Si14 silicon
Magnetic Resistant?	Yes, up to 15,000 gauss
Chronograph System	Column wheel
Hand Count	7
Functions	Central hours; central minutes; central chronograph seconds;small running seconds at 9:00; pointer date at 9:00; chronograph 12 hours and 60 minutes subdial at 3:00; moonphase indicator at 6:00
Hacking Seconds?	Yes
Finishing	Rhodium plated, Geneva waves in arabesque
Country of Manufacture	Switzerland, Swiss made
Known Models	Omega Speedmaster Moonphase (Ref: 304.33.44.52.03.001 Blue Side of the Moon) (Add your watch to the comments below…)

The Omega caliber 9904 is an automatic chronograph watch movement with a moonphase complication. It is also the first Speedmaster movement to be certified as a Master Chronometer. This caliber was introduced in 2016.

In Omega’s own words:

“Thanks to its Master Chronometer certification, the industry’s highest standard, the calibre 9904 signals another revolutionary step in OMEGA’s chronograph precision and excellence. The self-winding movement includes a column wheel mechanism and Co-Axial escapement for greater long-term performance. The movement, along with the watch itself, is tested according to Master Chronometer certification processes approved by METAS. Resistant to magnetic fields reaching 15,000 gauss, it features a silicon balance-spring and functions that include a moonphase complication. The movement has a rhodium-plated finish with Geneva waves in arabesque.” –Source

Some of the topics covered in this caliber listing:

Cal. 9904 VS 9905:

There is a similar caliber 9005 with the main difference being that the 9905 has a rotor and balance bridge made from 18K Sedna gold (source).

Moonphase Indicator:

On standard models, the moonphase indicator at 6:00 features a photo-realistic portrait of the moon.

There are special models with different renditions of the moon image, however, despite having various moon depictions, the caliber number is still the same 9904, but with a different part number for the moonphase disc.

What is the 29.5 moonphase marker?

You may also notice on the dial side that the moonphase indicator has markers for 0, 15, and 29 1/2. Omega explains below…

“A lunar month is slightly more than 29.5 days – a difficult time-span to manage for a standard gear train. But this model manages the task with its highly-accurate mechanism and only needs a simple adjustment after 10 years.” –Source

With regards to the same caliber’s ability to manage the lunar phase display, Omega quotes the adjustment time-frame differently:

“A brief astronomy lesson: a lunar month is not 30 days, but slightly more than 29.5 days. A difficult time-span to manage for a standard gear train, but OMEGA’s Moonphase is up to the task. In fact, the mechanism requires only a single correction every 122 years to realign the display to the position of the moon.” –Source