The Valjoux calibre 72 (72C) represented a major milestone in the development of complicated wristwatch-sized chronographs. It had an extraordinarily long production period, from 1938 to 1974. The 1940's were the heyday for wristwatch chronograph innovation, with all the major manufacturers working to add an hour register to their chronographs. The Valjoux 72C (calendar) includes the Day, Date, and Month. When servicing a Valjoux 72, it is important to understand that there were design changes to these movements, not all of which were formally published. This Wittnauer Valjoux 72C is a very early example made in the 1940's. These feature two pushers on the left side of the watch, one at approximately 10 o'clock and the other at 8 o'clock. The pusher at 8 is for advancing the date. The pusher at 10 advances the month and may-- or may not -- advance the day. Some 72C's feature the ability to 1/2-way push the 10 pusher to advance the day. And others, like this early version, do not have that function. Instead, the user must move the hands forward to set the day and then set the rest of the watch-- even some modern movements today require this manual method of advancing the day, so it isn't that unusual. However, if you are unaware of the 72C design differences, you may assume your watch has a problem that it doesn't. The dial side picture shows a red arrow at about 6 o'clock. This lever is "single jointed" and thus only changes the month. A "double jointed" lever was later produced that allows the day to be changed with the same pusher. This movement was also made with both flat and breguet hairsprings. The movement shown here features a breguet overcoil. When I serviced this movement, the first thing I noticed was a previous watchmaker had replaced the correct breguet regulator with an incorrect flat hairspring regulator. They are different and not interchangeable. This error of course was only the beginning, because you can guess from my past posts what I observed next-- a fouled hairspring requiring a good deal of work to bring-back to excellent operation. The other two arrows show the wheels involved in delivering the hour register capability. These are dial-side, just as they are on the Omega 321/Lemania 27ch and others. These wheels take a beating over time due to the friction-based design and so I always inspect these right away when servicing an hour register-based chronograph. I always liked these Wittnauer 1940's chronographs, in part because of the way they wrote their logo. This is an original dial, the logo was written this way. It almost feels like it is done by hand, something I have come to enjoy as part of their 1940's charm.