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It's a bit comlicated, but here you go...
Jan 25, 2007,05:52 AM - (view entire thread)

Hi Steve,
it's a bit complicated, but quite simple at the same time smile

Please take all below with a grain of salt - it's what I believe is correct, but I don't consider this authoritatively.

All movements you  mention share the same roots and in this case "roots" means they share the same going train.

The Valjoux 13''' family started out with a monopusher chrono which I believe was  called cal. 13 only.

This was soon changed into cal. VZ  - a two pusher chronograph movement (seconds on "9") with minute counter (on "3"). 
That's the base for the PP ref. 1518  in your first picture as well as for other PP "simple" chronos and rattrapantes of that period. The
perpetual calendar part is PP (and has nothing to do with Valjoux's own calendar versions, which are simple calendars) .

Valjoux's cal.  VZ  is the base of a whole family of iterations, mainly :
  • VZ - base chrono with minute counter
  • VZH - chrono with minute and hour counter
  • VZQ - chrono with minute counter and simple calendar
  • VZHQ - chrono with minute and hour counter and simple calendar

I'm unsure about an eventual calendar with moonphase version, but have seen references towards at least VZHQL which would mean  chrono, minute and hoour counter and calendar with moonphase. But as said, I'm not 100% sure I've seen one in the flesh ( the simple versions are becoming rare, the calendar version even more ).

The next generation had soome changes to the chrono levers and springs, but going train and basic design remains - cal names changed into:
  • 23
  • 72
  • 23C
  • 72C
  • 88 - minute and hour counter, calendar with moonphase

Even later there were an extended and partially revised range and the cal. numbers got  three digit. Slightly altered beat rate was one
modification, but also flyback  and a simple date with cut out at 6 for cal. 23 example. There are many and I'm not able to list them all out
of the top of my head.


A good and reliable going train of a chronograph movement was always considered a good base for a high precision time only as well -  no wonder as the "power supply" is designed to serve for a complicated (and power consuming) movement, with reducing friction and complications time keeping can only improve. The time only with calendar calibers 78 and 90 are such "reduced" versions - 78 is calendar only and 90 with the calendar part of cal 88 which means full calendar with moonphase.

Some manufacturers, like PP and Audemars for good reasons chose this base caliber for their ww precision timekeepers. In later 40ties this caliber perfectly fitted  the newly created ww movement observatory category oof 30mm movements.  From PP I only know the VZ normal  version with seconds at 9 - basically it's the stripped version of the chronograph. AP used three versions as time only, what they called the VZAS, VZAS and VZSSc.  VZAS is time only with seconds at "9", VZSS is time only with seconds at "6" .

I believe the last "S" in AP terminology  stands for seconde. For  VZSS I believe the first "S" indicates "savonette" for the small second at v"6".
The VZSSc is the savonette version with an indirectly driven center sweep second.

The difference between VZAS and VZS base is mainly a swapped barrel and crown wheel position - they simply change place. The result beeing seconds on "9" (for the "original" chronoo going train layout) versus small seconds at  "6" for VZSS, the savonette layout.

BTW, the last picture (which I believe is from Osterhausens ww chronometer book) is an error - the movement shown is the savonette version (VZSS) whille  the pictures only show the seconds at "9" former chrono  base layout (or one could also say Lepine, as originally this chrono layout  was also used in open face pocket watches).

One should also note, that AP and PP both used a secial mainplate with this Valjoux based movements - among others it allows for solid pallet  bankings (required by the geneva seal for example) and is well recognizable by the different pallet bridge (also steel instead of 
brass here).

Hope this helps a bit - and of course all corrections and additions more than welcome!

Best regards

Suitbert

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