Longines' representative chronograph movement! The greatness of Cal.30CH and Cal.13ZN

Longines Chronograph 13ZN sales page

Longines Cal.13ZN

In 1936, some 23 years after the production of the 13.33Z chronograph, Longines began producing one of the most technically advanced chronographs of its time: Caliber 13ZN.
Longines wristwatch developed the first chronograph (the 13.33Z), which was the first chronograph mechanism with flyback function.

The 13ZN had 17 jewels.
It had a diameter of 29.80 mm, a height of 6.05 mm, beat at 18,000 vph and was fitted with a Breguet balance spring.

It is perhaps no coincidence that the flyback mechanism was developed at Longines since the beginning of the 20th century, with a strategic focus on aviation and sports.

But before we delve into the movement, what is the flyback function and what is its purpose?

Engaged Chronograph

disengaged chronograph

A typical chronograph has a tooth on the zero-reset hammer that is blocked by the column wheel when the chronograph is running to prevent the chronograph from being accidentally reset.

Therefore, the reset hammer can only be dropped when the chronograph is stopped and the column wheel has rotated slightly to create an opening.

The photo above shows the watch with the chronograph running.
You can see that the column wheel engages with the reset lever.
The photo below shows the chronograph when stopped, allowing the column wheel to rotate and the reset lever to fall.

Longines Caliber 13ZN

The flyback function, on the other hand, works by triggering the reset mechanism while the chronograph is still running.
The most noticeable mechanical difference is that the reset hammer has a missing tooth on the head (circled in red).
This allows for unhindered movement to reset the chronograph even while running.

At the same time, the flyback process disengages the chronograph clutch from the chronograph wheel while the reset button is pressed, then re-engages it after it is released (circled in blue).
It may sound simple on paper, but consider that virtually no other manufacturer attempted to create a flyback mechanism in a chronograph until chronographs produced for the French military two decades later.

Yet they were on board with either the Valijouxm or Lemania movement.

Why go to all the trouble and research to develop a mechanism for a flyback when we understand how it works?

Charles Lindberg

Imagine you need to time two successive events in a very precise way.
For example, a pilot must fly north for exactly 30 seconds, then fly east for 20, and then north for 15 seconds.

Other chronographs at that time require you to press the start, stop and reset button three times in rapid succession.

This is a behavior that can reduce measurement accuracy.

A Breitling invention in the mid-1920s allowed the start/stop and reset mechanisms to be separated into two buttons, but this did not solve the problem.
But on the 13ZN, a single press of the button at 4 o'clock is all that's needed.
This is the beauty of movement.

In addition to the movement, the 13ZN was made with a variety of cases and dials.
This is one reason why collectors are so obsessed with this watch.
They came in both steel and gold cases, ranging from 34mm to 38mm, excluding the crown.

The gold cases come with snapback casebacks and hinged, and a variety of lug designs, from curved to straight lugs, in 14K or 18K.
All paired with beautiful dials.

The example above shows the sophistication of the dial design that accompanies this movement.

Longines 13zn

But the most interesting thing about the 13ZN is that it comes in a waterproof steel case.
It is connected to an Italian made "Tre-Tacce" or "Sei-Tacce" screwed case back with either 3 or 6 notches.
They came with either a button pusher or a mushroom shaped pusher.
The latter was actually patented by Longines.

These are usually the larger, more modern 38mm size and look great on the wrist.

These are not dress watches but tool watches meant to be used in the field.
For example, there is a set of caliber ZNs being sold to a Romanian county, many of which are billed to Longines' US partner, Wittnauer, for sale to personnel connected to the aviation industry as well as the military.

This Christmas

Finally, note that this was not an inexpensive watch in the 1940s, when it sold for $125, according to the catalog.

Compare this to the prices of two offered by the Henri Stern Watch Agency in New York.
One is Universal Genève and the other is Patek Philippe.
By comparing you will be able to see the difference in prices.


The first and earliest 13ZN was called the "transitional 13ZN" and had a monopusher and an enamel dial.
These were likely produced between 1936 and 1939, making them the rarest version of the 13ZN in the world and were a transition between the 13.33Z and the 13ZN.

Here we can see that there is only one pusher at the 2 o'clock position.
This version of the 13ZN, with only one pusher, does not have the flyback function and therefore functions similarly to the 13.33ZN described in the previous section.

There is also another version of the 13ZN that does not have the flyback function, but it does have two pushers.

If you open the watch and look at the movement, notice that the reset lever has teeth that prevent the chronograph wheel from resetting while the lever is engaged.
13ZN without the flyback function

These 13ZNs have been sold divergently and yet very little is known about them.
It is also not known why the flyback function was intentionally removed.

At this point we come to one of the most wanted Longines in the world: the caliber 13ZN-12.

This is essentially the caliber 13ZN, but the hour counter replaces the minute counter at the 3 o'clock position.
The minute counter now encompasses the entire dial, with a separate hand tracking the elapsed minutes.
Instead of resetting two counters like the 13ZN, you need to reset three counters: seconds, minutes, and hours.

This significantly raises the level of complication in the movement and is one of the reasons why these watches are so desirable by collectors.


These were cased in both gold and steel, with the steel reference 23086 being the most common 13ZN-12 (with a total of 500 movements made in total).

These came in cases roughly 40mm in size.
With its button pushers and six-notch screw-down caseback, it combines military seriousness with a slightly playful casual feel thanks to the red minute hand.

The rectangular pushers have less case, and the gold has even less case.
These are exceptional watches, both in design and functional sophistication.
Great role models are always needed.

Longines Cal. 30CH

The 30CH had exactly the same functions as the 13ZN.

It was made up of 17 jewels, had a diameter of 29.80mm, a height of 6.20mm and beat 18,000vph.
The movement vent was typically fitted with a shock guard ring, also found on the majority of the 13ZN-12 movements.

Longines caliber 30CH

Similarly, notice that the reset lever has no teeth (circled in red).
When the reset lever is operated the central chronograph wheel is reset (red arrow).
At the same time, the lug (circled in orange) pushes up the wheel (orange arrow) which starts the chronograph, and then moves it back down when the reset lever is released, restarting the chronograph function.
This is to generate a sequence of operations that enables the flyback function.

The watch that comes with the 30CH is designed to be "sportier" than the 13ZN, reflecting the style of the era.
Therefore, many of the 30CHs are made from steel and usually come with a waterproof case and button pushers.

The gold model of the 30CH can also be found with a waterproof case.
This is a style not commonly seen on the 13ZN.

The 30CH (and its variants) was produced for around 20 years until the 1970s, when Longines was taken over by Ebauches, ceased in-house production, and instead purchased Ebauches from Barouge.
This strategic decision not only unfortunately led to the extinction of beautiful chronograph movements, but ultimately proved futile in the face of the quartz crisis.


In the same group as the 30CH were two other models: the L530 and the L538.

The first member, caliber L530, is essentially the same movement as the 30CH, but housed in a dive watch case.


Longines Diver 1967

The design of this particular model was also the inspiration for the Longines Heritage Diver (L2.808.4.52.6), with the addition of a date display at the 5 o'clock position alongside a counter.

Longines Nonius flyback

Longines caliber L538

The final member of this group is the caliber L538.

This was a modified 30CH without the secondary seconds counter at 9 o'clock.
This was also the last in-house chronograph movement designed by Longines.
As the precision of chronograph mechanisms increased, movements could time events accurately to 1/10 of a second (instead of the previous 1/5th).

The 30CH movement also sometimes occurred without the flyback function.
Notice the movement below, where the reset lever has teeth, compared to a typical 30CH movement.

Longines 30CH without flyback mechanism

Again, there is little information available as to why such a change was made.
If there is anyone who knows, I'd like to know.

As such, Longines' calibers 30CH and 13ZN are truly magnificent watches that are loved and popular by many people.

Longines Chronograph 13ZN sales page