7750 — the automatic chronograph that took over the trade

In one line

The most-produced automatic chronograph in Swiss watchmaking: cam control, 25 jewels, 30 mm across, 48 hours of reserve. It exists today because in 1975 the engineer who designed it refused to scrap the tooling.

First things first: you can spot it from the dial

There is no need to open the watch. The subdial layout of the 7750 is so distinctive that it has become the standard face of the Swiss chronograph, and that alone will get you the right answer most of the time.

That asymmetry is not a styling decision. It is where the wheels of the chronograph land, and the dial was drawn over the top of them. Next time three chronographs from three different brands look suspiciously alike, you know why.

One warning: the layout tells you which architecture is underneath, not who made it. Since ETA stopped selling outside the Swatch Group, plenty of watches wearing this face run the Sellita SW500, a cloned 7750.

Cam against column wheel: here the cam won

On the Speedmaster, going from column wheel to cam was a cost cut, and your finger can tell. On the 7750 the cam was there from day one, and it is the reason the movement exists at all. Longines went the other way thirty-five years later, working from this same base.

A cam is a flat part that distributes the pusher's orders; a column wheel does the same job with a toothed one, dearer to make and dearer to adjust. Under the finger, the column wheel feels crisper. As a timer, neither is better than the other.

If you want to see what the 7750 became once Longines fitted a column wheel, we have its page: Longines calibre L688.

Where it comes from

Valjoux handed the project to Edmond Capt, a twenty-four-year-old engineer from the Vallée de Joux who had spent a year at Rolex. He started work in 1970, taking the hand-wound Valjoux 7733 as his starting point. The first examples ran in 1972; the first units reached customers in 1973.

He designed it with the help of a computer, and that part of the story is usually told wrong. Valjoux had no computers. Capt travelled to Neuchâtel, where the technical director had access to the only machine going, and used it to digitise the drawings and simulate the kinematic sequences. For 1972, that was science fiction applied to a chronograph.

Then quartz arrived. Orders stopped in 1975, management wrote off mechanical watchmaking and gave the order to destroy the machinery, the drawings and the tooling for the 7750. The man told to carry that out was Capt himself. He didn't: he boxed up what mattered and put it away. When mechanical watches came back in the mid-1980s, the 7750 could come back with them, because it still existed in crates.

Proof that the return would stick came in 1985, when IWC launched the Da Vinci ref. 3750 with Kurt Klaus's perpetual calendar built on top of a 7750.

Why it matters

It was tough and it was available, so dozens of brands took it as the base for chronographs of their own — from pilots' watches to high-end pieces dressed in house finishing over the same architecture. Along with the hand-wound Valjoux 72 that came before it, it is one of the two movements every collector of Swiss chronographs meets again and again.

Three things almost nobody knows

• The famous wobble is not a fault. The rotor of the 7750 turns both ways but winds in only one. Spinning free, it meets no resistance, picks up speed, and the moving mass makes the watch shift in your hand of its own accord. Owners have been taking it to the watchmaker over this for forty years. It is normal. A gritty noise is not.
• The oscillating pinion is not Valjoux's. The part that couples the going train to the chronograph when you press was patented by Edouard Heuer in 1887. Eighty-six years before the 7750, and still doing exactly the same job.
• The Da Vinci's perpetual calendar is 81 parts sitting on this movement. Kurt Klaus built it in 1985, using the date change of the 7750 itself as the motor. From that one impulse it drives day, month, year, decade, century, millennium and moonphase, shows the year in four figures out to 2499, and sets in full from the crown, with no correctors in the case band. Until then, perpetual calendars were adjusted by poking the side of the case with a pin.

Technical data

What a watchmaker checks before buying one

Start with the pushers. Cam control has a feel of its own: the first press goes in with a certain firmness, and all three functions — start, stop, reset — should weigh about the same. A 7750 that starts under a little finger but needs a thumb to stop has a badly adjusted cam or hammer spring.

Then the reset. All three hands should drop to zero together and land dead on it. The hour counter gives itself away first, because it is dragged along from the minute counter and is the first to drift. Try it three times running, not once.

The rotor deserves a paragraph of its own. Some noise and some wobble is normal — the reason is above. What is not normal is vertical play in the rotor, or a dry scraping sound: that is the bearing, and although the part is cheap, the movement has to come out of the case to reach it.

And the question that moves the estimate: is there a module on top? A good share of 7750 watches carry not a bare 7750 but a 7750 with a perpetual calendar, a GMT or a moonphase built over it. Servicing the base movement is routine work. Servicing the whole assembly is not. Ask before you buy, not after.

Watches that used it

• IWC Da Vinci ref. 3750 (1985) — Kurt Klaus's perpetual calendar
• IWC calibre 79350 — 7750 base, chronometer-certified
• Breitling calibre 13
• TAG Heuer Calibre 16
• Sinn, Fortis, Hamilton and Chronoswiss, among many others

The column-wheel cousin, made to order for a single brand, is the Longines calibre L688.