COMPLICATIONS!

Eight hands and three discs total make the following functions possible:

1. Hour of the day--12 hrs
2. Minute of the hour
3. 24 HR subsidiary hand
4. subsidiary seconds hand
5. Chronograph hand (seconds)
6. Chronograph Minute register with Jumping hand
7. Chronograph Hour register with 12 hour capacity
8. Day of the Week window
9. Month of the Year window
10. Date pointer by hand
11. Moon phase indication
12. Tachometer bezel for calculation of speeds, complements chronograph

I painted the tip of the seconds hand red in order to easily distinguish it from the 24hr hand.

Located at 9 o'clock, this is the only moving second hand when the chronograph mechanism is not engaged.

The 24hr hand plays a very important role when setting the watch (more on setting the watch further down). As I later point out, it is not advisable to set some calendar functions during  times when the gears and mechanisms are engaged in critical transitory calendar phases, but I will describe that below.

Another advantage of the 24hr hand is that it makes it impossible to the time wrong (i.e., set for noon at midnight or voice versa).

Located at the 12 o'clock position, within the chronograph minute-register sub-dial, are two small windows on the dial that reveal the Day of the Week and the Month in progress.  Also on this dial is the "jumping" minute register.  It's fun to watch this hand "jump" as the central chronograph hand does one revolution. Again, the tip of this hand has been colored red for legibility and aesthetics.

Here you can see the windows in the dial, only minutes before the day-date mechanisms display transition.

For legibility, against the midnight blue of the "sky" on the moon phase disc, I have painted the tip of the hour register  red.

This is what sets my Omega Speedmaster apart from the current production models....Located at the 6 o'clock position, this subsidiary dial has a window through which the current moon phase can be viewed.  (Read about the accuracy of this indicator at the bottom of the page)

Also located in this subsidiary dial is the chronograph hour register hand.  It is very useful after 30 minutes into the operation of the chronograph, since it is only here that you see how long it has been since the chronograph function was engaged.  It can register up to 12 hours after which it repeats its cycle.

For me, what makes this watch so great are it's many complications, of which the "Full Calendar" is certainly one. Granted this is not a "Perpetual Calendar" where one does not have to adjust months with 28,29 or 30 days, but instead this calendar operates much like classic calendar plates. In any event, I find it an entertaining moment to watch these transitions at the end of the day.

Although the changes begin to occur around 9 PM, they only become obvious after 11:00pm when the Date hand, of which I colored its tip red like classic watches, begins its gradual transition.

Soon after, the Day disc begins turning gradually as well.  As you can see from the illustration on the right, one can see the system is in transition.  At midnight, the Date hand finally "drops" into the position, while the Day disc takes an additional 5 minutes to finish its voyage. 

The Valjoux 7751/modified Omega 1151
CALENDAR MECHANISM

All of the action is located on this beautifully finished calendar plate. Which is where the Valjoux 7751 (Omega 1151) and  7750 (Omega 1152) differ. 

It would be important to note that not all Valjoux 7751s are finished like this, since Omega has additional functional and aesthetic finishing (although they do not have exhibition backs) and some of the parts are unique on its movements. 

It would also be important to mention that the current line of Day-Date Speedmasters (caliber 1151) do not have the moon phase drive mechanism, nor its many components in place.  The Omega movement corresponding to the Speedmaster Classic of the early 1990s was the Omega 1150, which is a 17 jewel version of the Valjoux 7751 with guild-finish.

          The Month finger is on a disc attached on top of  the date wheel.  After the 31 day cycle, it engages with the Month wheel which transitions the Month disc to the next month in pretty much the same manner that the Day disc operates. It is important to note that both the  Day and Month discs are held in place with jumpers (not in view) that look like the Moon phase Jumper.

The Moon phase Yoke, which is held in place by two springs, is activated by the revolving of  the odd-shaped perimeter of the Calendar wheel. The Moon phase Corrector and the three Jumpers for each of the three discs (Day, Month, Moon) also have similar springs which hold them in place.  When the calendar wheel moves into a certain position, the shape of the calendar wheel's perimeter pushes the Moon phase Yoke which moves with "See-Saw" action, driving its other end into one of the teeth of the Moon phase Disc.  This simple action, which takes place apparently from 3 am to 4 am, perfectly advances the Moon phase Disc one tooth (1/59th of a full cycle).

Adjusting the calendar is somewhat of a pleasure as well, since it is not complicated and it can be done very quickly via the crown and one single case button located at 10 o'clock.

Of course one must take special caution when it comes to making any type of date adjustment during the time that the calendar is in transition to avoid the possibility of jamming or damaging the movement. This is one of the occasions in which the 24 hr hand comes in handy.

The crown has three positions.  In the "in" position the chronograph is water resistant, and can be manually wound.  In position two, the crown acts as a date and month corrector as well as moon phase corrector. And, in position three, the time can be set.  In this position, the seconds stop as well so that the timepiece may be synchronized with an official time signal.

HOW CALENDAR CORRECTION WORKS

In order to make adjustments to the Date, Month and/or Moon phase, one must pull the crown out to position two.  In this position, the Date/Moon phase Corrector Star takes center stage.   Its clever design allows for a rocking motion depending on the direction the crown is turned.  Thus, if the crown is rotated clockwise, the Moon phase Corrector Star moves down, and engages with the Moon phase Corrector itself, pushing it down with each turn of the star, causing the Moon phase Jumper, that holds the Moon phase disc in place with light pressure, to retrieve allowing the corrector to advance the Moon phase disc  one tooth at a time.  If the crown is turned counterclockwise the Date/Moon phase corrector moves left to engage with the Date wheel, efficiently advancing it.  Since the Date Wheel drives the Month Wheel (once every 31 day cycle) via the Month Finger, there is no need for additional devices to adjust the month, as it happens automatically.

The Day of the week can be easily adjusted by pressing the recessed case-band button located at 10 o'clock.  One single push of the button and the Day advances instantly.

Based on the data that the real moon phase is 29 days 12 hrs 44 minutes and 3 seconds, and that this watch, like most moon phase discs, has 59 teeth advancing at the rate of 1 tooth per day (reflecting two 29.5 day moon cycles on the disc), the indicator would be fast by 88.1 minutes every 59 day revolution.

There are 365 days in a year, so the revolving disc does 6.1864406779661 cycles in one year, which multiplied by 88.1 (minutes fast per cycle) equals 545.0254237288 minutes or 9 hours, 5 minutes and 1.525423728 seconds fast per year.

99.8963% Accurate

How often does it need to be corrected?

Since the moon phase disc advances at the rate of 1 tooth per 24 hrs, it would take 24 / 9.0837570621466 or 2.6420785844231 years for it to be "fast" by one day (i.e., one tooth on the disc)

It would have to be corrected every 2 years, 33 weeks, 3 days, 36 minutes, and 30.23911584 seconds.


NOTE: this is a regular 365 day year I am talking about... not LEAP year ;)

The Current Moon phase

by Virtual Reality Moon Phase Pictures