In-Depth: A Detailed Look At Early Longines Chronographs, Including The Legendary 13ZN

PH Zhou is a student at the Massachusetts Institute of Technology, where he studies economics and computer science. He is a devoted enthusiast of vintage watches – in particular early- to mid-20th-century chronographs.

When we talk about vintage chronograph movements, there are many deserving of our attention – from the relatively common Valjoux 72 that powers anything from a Rolex Daytona to a Gallet Multichron 12, to the exceedingly rare and complicated Caliber 13-130 that resides in a Patek 1518 Perpetual Calendar Chronograph. However, as much as it is a sin to claim this for the latter, neither of the two movements we just mentioned are truly "in-house," since the Caliber 13-130 is still ultimately based on a Valjoux ebauche. In fact, the number of companies that produced both watches and movements were few and far between.

One truly "in-house" chronograph movement began its development in the 1920s, with changes, upgrades and different modifications taking place until it was finally phased out in the early 1970s. Of course, we are talking about the Longines caliber 13ZN, one of the arguably most beautiful chronograph movements ever developed, until perhaps the release of the A. Lange & Söhne calliber L951 inside the Datograph.

Surprised? While Swatch has positioned the Longines brand rather differently since its acquisition in 1971 by Ebauches S.A. (the precursor to Swatch Group), Longines was one of the most respected manufacturers back in the 19th and early- to mid-20th century, especially of high precision chronographs.

A brief glance at Longines’ logo – the winged hourglass – can probably give us some hints as to the focus of the company on aviation. To that end, Longines was appointed the official supplier for the International Aeronautical Federation (IAF) in 1919, which enabled the company to be involved in many aeronautical expeditions during the early 20th century. The most famous of them was Charles Lindbergh’s solo, non-stop flight from New York to Paris in his aircraft, the "Spirit of St. Louis," in May 1927.

The second activity that prompted the developments of technologically advanced and sophisticated chronographs was Longines’ involvement in sports timing. For instance, in 1926 Longines timed the International Equestrian Competition in Geneva, and in 1933 the Brazilian Grand Prix as well as skiing world championships in Chamonix.

While Longines also developed many elegant and classic time-only watches during its history, the largest focus for "complicated" watches was on chronographs. 

The company’s strategic focus on these two market segments resulted in a research effort directed almost exclusively to chronographs. While Longines also developed many elegant and classic time-only watches during its history, the largest focus for "complicated" watches was on chronographs. For instance, consider that Longines did not create any diver watches until the late 1960s, or watches with a simple calendar or moon-phase complication, in contrast to many of its contemporaries such as Universal Geneve or Jaeger-LeCoultre, to name a few.

However, the strategic decision to create the best chronographs did result in some of the most advanced and beautiful movements of the age in both pocket and wrist watches. While the marvelous calibers made for the pocket watches (such as the 19.73N Rattrapante) can be left for another day, we begin our historical journey with the 13.33Z – one of the first chronograph movements ever developed for a wristwatch.  

Longines Caliber 13.33Z

The caliber 13.33Z was first developed in 1913 and featured 18 jewels, a diameter of 13 lignes (29 mm) and height of 6 mm, beat at 18,000 vph and utilized a Breguet hairspring. It had a crown that was used for winding the watch and served as a pusher for the chronograph. The first push starts the chronograph, the second stops it, and the third resets, and the cycle repeats. In the earlier versions of the movement, the crown could not be used in a "pulled-out" or "extended" position – pressing a small stylus at the 2 o’clock position switched the functions of the crown, allowing it to change the time. While most of the 13.33Z movements had the integrated pusher at the 3 o’clock position, there were also the rarer variations that had a pusher at 2 o’clock.

Why is this movement significant? It was the first chronograph for the wristwatch.

I’m not sure how more monumental this can be. Consider that the chronograph function was, prior to 1913, restricted to pocket watches. In order to actually use the chronograph and keep track of elapsed time, you would need to hold the pocket watch in one hand. But what if you’re faced with a situation where you might need a chronograph and the use of both your hands (perhaps to fly a plane or hold a rifle), it would be a lot more effective to have a chronograph on one's wrist.

It is hence no coincidence that the first of these watches were meant for military use. History gives us a reason for these developments – we're talking about the period leading up to World War I.

The 13.33Z caliber was cased primarily in gold and steel, paired with beautifully decorated enamel dials with hues of blue and red. Interesting fact: enamel dials, while prone to cracking, actually do survive far better than normal dials if taken proper care of. There is typically very little "patina" on enamel, as compared to normal dials, which oxidize more easily. Hence many of these watches from the early 1910s up till the 1930s actually remain in absolutely stunning condition – especially considering that they are almost 100 years old.

There were many variations of the dial offered, from simpler versions with just Arabic numerals to ones with tachymeters, pulsometric scales or telemeters. The watch above shows a pulsometric scale used to measure a patient's pulse. You would start the chronograph as you begin measuring the pulse, and stop after 30 beats. The number that the sweep seconds hand is pointing to would be the patient's heart rate. The earlier versions of the dials, especially those on enamel, came with the cursive Longines font instead of the serif.

Another interesting fact: these watches, perhaps due to influence from the pocket watches of the time, typically came in cases with double case backs – not dissimilar to how a pocket watch might be constructed. Engravings on the case backs were also common especially for the watches cased in solid gold.

These engravings typically present the number of "Grand Prix" that Longines won up to the Barcelona Exhibition of 1929. These "exhibitions" were set up to be competitions for different watchmakers to showcase their watches and movements, especially accuracy and the degree of complication. By the date of production of the above example, Longines has won five "Grand Prix" (Antwerp in 1885, Paris in 1889, Brussels in 1897, Paris in 1900, Milan in 1906). The next Grand Prix that Longines won was in 1914 in Bern, and since that was not reflected in the engraving, and considering that the 13.33Z was first produced in 1913, it makes the above example one of the earliest 13.33Zs ever produced. Longines would go on to win 10 "Grand Prix" in total (the last at Barcelona 1929), more so than any other manufacturer.

Collectability

While prices of 13ZNs have been steadily increasing, the 13.33Zs, in our opinion, are still somewhat underpriced and feature less prominently in the minds of collectors despite their stunning movements and dials. You would probably be able to find a mint condition 13.33Z under $10,000, with most residing in the 6-8k range. There is also less of a difference in prices between steel, gold (and silver) cases as compared to the 13ZNs. One thing to note: be very wary of enamel dials, which may crack easily during shipment (you might be in for an unexpected shock if the watch arrives with hairline cracks in the dial due to improper packaging). Also, since most of these watches came with hinged backs, be aware that the hinge may have been previously broken, and then fixed by a jeweler.

Another key thing to pay attention to is making sure the serial number stamped on the movement match with the number stamped on the case. For instance, the two pictures below are from the same watch, and the serial numbers do match.

It is further worth mentioning that Longines has fantastic customer service that can provide you with information from their archives if you have the serial number of the watch, usually within 48 hours of your request. The information would include the caliber of the movement; who, when and where it was invoiced to; and the reference number and material used for the case. This allows you a great way to check the authenticity of the watch in question, especially since re-casing of watches was common in the early 20th century. For instance, an originally gold case might have be melted down and the watch movement and dial put in a cheaper, likely steel, case.

Additional Variations

But to digress for a moment – while this was the final, and perhaps more well-recognized form of the 13.33Z, there was in fact a similarly-named, time-only caliber 13.33Z that preceded this movement. Perhaps it might have been an administrative decision to rename the time-only movement (which also looks very similar to an early version of the caliber 13.34), but there nonetheless exists a twin 13.33Z movement, with a dial to strangely reminiscent of a similar one on the 13.33Z chronograph.

Longines Caliber 13ZN

After an approximately 23-year production of the 13.33Z chronograph, in 1936 Longines began to produce one of the most technologically advanced chronograph movements at the time – the Caliber 13ZN. As we mentioned at the beginning, Longines developed the first chronograph for the wristwatch – the 13.33Z – but this was the first chronograph mechanism equipped with the flyback, or retour-en-vol, function. The 13ZN had 17 jewels; a diameter of 29.80 mm and height of 6.05 mm, and beat at 18,000 vph, and was equipped with a Breguet hairspring.  

It is perhaps no coincidence that the flyback mechanism was developed at Longines given its strategic focus on aviation and sports since the early 20th century. But before we describe the movement in detail – what is the flyback function, and what was its purpose?

In typical chronographs, there is a tooth on the reset-to-zero hammer that is blocked by the column wheel when the chronograph is running in order to prevent any accidental reset of the chronograph. Hence only when the chronograph is stopped, and the column wheel slightly rotated to create an opening, can the reset hammer drop. The photo on the left shows the watch when the chronograph is running – notice that the column wheel is in the way of engaging the reset lever. The photo on the right shows the chronograph when stopped, where the column wheel rotates to allow the reset lever to fall.

While it may sound simple on paper, consider that no other manufacturer attempted to produce a flyback mechanism in a chronograph until 20 years later with the advent of the Type XX chronographs produced for the French military.

A flyback function, on the other hand, allows for the reset mechanism to take place while the chronograph is running. The most obvious mechanical difference would be the lack of a tooth (circled in red) on the head of the reset hammer, which hence allows it an unobstructed movement to reset the chronograph even when it is running. At the same time, the flyback process must also disengage the chronograph clutch, pushing it away from the chronograph wheel while the reset button is pressed, then re-engaging it once it is released (circled in blue). While it may sound simple on paper, consider that no other manufacturer attempted to produce a flyback mechanism in a chronograph until 20 years later with the advent of the Type XX chronographs produced for the French military. Even then, they were mounted on either a Valjoux or Lemania movement.

Now that you understand how it works, why go through all that trouble and research to develop such a mechanism?

Imagine you need to time two consecutive events in a very, very precise manner. For instance, a pilot needs to fly north for exactly 30 seconds, then east for the next 20, and north again for 15 seconds. In other chronographs at that time, one would need to press the start-stop-reset button 3 times in rapid succession – a process that could throw off the precision of the measurement. A Breitling invention in the mid-1920s allowed for the separation of the start/stop and reset mechanism into two buttons, but that did not solve the problem either. But in the 13ZN, a single press of the button at 4 o’clock is sufficient – and that is where beauty of the movement lies.

Besides the movement, the 13ZNs came in a wide variety of cases and dials, another reason why collectors go crazy about this watch. They were cased in both steel and gold, with cases ranging from 34 mm to 38 mm, excluding crown. The gold cases came in either 14K or 18K with snap-back case backs and a variety of lug designs – from hinged, to curved, to straight lugs, all paired with stunningly beautiful dials. The examples above show the sophistication of dial design that came with this movement.

But the most interesting 13ZNs reside in waterproof, steel cases, coupled with a three- or six-notch screw down case back, also called "tre tacche" or "sei tacche" in Italian. They came with either button pushers or mushroom pushers; the latter were actually patented by Longines. These usually came in larger, more modern 38 mm sizes, which sit wonderfully on the wrist. These are not designed to be dress watches, but rather tool watches that were meant to be used in the field. For instance, there is a set of caliber 13ZNs sold to the Romanian military, and many were also invoiced to Wittnauer, Longines’ partner in the U.S., to be sold to personnel involved in the military, as well as the aviation industry.

Lastly, note that this was not a cheap watch by any means at the time it was sold - $125 in the 1940s, according to the catalogue. Compare this to the prices of Universal Geneve, one of two brands carried by the Henri Stern Watch Agency in New York - the other brand that they carried was Patek Philippe.

Variations

The first and earliest 13ZNs are referred to as "transitional 13ZNs" and came with monopushers and/or were cased with enamel dials. These are likely produced between 1936 and 1939, making them some of the rarest versions of the 13ZNs in the world, and they were a transition between the 13.33Z and 13ZN. We featured one of them previously, and you can see how there is only a single pusher at the 2 o’clock position. This version of the 13ZN with only a single pusher does not have the flyback function and hence functions similarly to the 13.33Z, as described in the previous section.

There is another version of the 13ZNs that also came without the flyback function – but with two pushers. If one opens up the watch and looks at the movement – notice that there is a tooth on the reset lever that prevents the lever from resetting the chronograph wheel while it is running.

There is little that is known about these 13ZNs, or why the flyback function was intentionally removed, but they do pop up sporadically for sale.

At this point, we come to one of the most desired Longines in the world – the caliber 13ZN-12. This is essentially a caliber 13ZN, but an hour counter takes the place of the minute counter at the 3 o’clock position. The minute counter now encompasses the entire dial, and a separate hand tracks the elapsed minutes. Instead of resetting two counters in the 13ZN, the movement now has to reset three counters – the second, minute, and hour – and still possess the flyback functionality. This tremendously increases the level of complication in the movement and is one reason why these watches are so desired by collectors.

These came in almost 40 mm cases, with button pushers and a screw-down case back with six notches, combining a military seriousness with a somewhat playful casualness due to the red minute hand. There are fewer cased with rectangular pushers, and even fewer cased in gold. These are absolutely stunning watches, both in design and mechanical sophistication, and great examples are rare and always in demand.

These came in both gold and steel cases, with the reference 23086 in steel being the most "common" 13ZN-12 (an estimated 500 movements were made in total). These came in almost 40 mm cases, with button pushers and a screw-down case back with six notches, combining a military seriousness with a somewhat playful casualness due to the red minute hand. There are fewer cased with rectangular pushers, and even fewer cased in gold. These are absolutely stunning watches, both in design and mechanical sophistication, and great examples are always in demand.

Collectability

A gold-cased 13ZN in good condition can be found between $8,000 and $10,000 today, with prices typically increasing with the size of the case. Steel-cased 13ZNs, on the other hand, may begin at $8,000 to $10,000 for a mid-sized, snapback example in good condition but up to $40,000 (or more) for oversized examples in mint condition. For reference, a good condition 13ZN-12 ref 23086 in steel would probably cost at least $50,000 to $60,000 – making it one of the most expensive Longines watches other than the unicorn-like Siderograph (see here and here) or A-7. Again, condition is king – an example in less perfect condition can be found at a significant discount.

A few caveats though – the 13ZN is one of the most commonly re-dialed examples for any vintage chronograph by Longines. The process of identifying an original dial is additionally complicated by the fact that Longines themselves had in the past restored dials as part of their service.

In general, you would want to see "open" 6’s and 9’s on both the main dial and sub-dials. The markings on the outer track should be crisp and the 3’s and 5’s should generally have flat tops. Also be on the lookout for the correct "Longines" font for the era. For instance, I have yet to see a 13ZN dial printed with the winged hourglass logo beneath on the dial – that was a style in the 1950s when the 30CH replaced the 13ZN.

Another method to check for the originality of the dial would be to look at the dial "feet." While this seems more anecdotal, most redials seem to come with “silvered” feet instead of “coppered” feet in the originals.

Beyond the dial, you should also want to see matching serial numbers on the case and the movement for the earlier versions of the 13ZN. Longines unfortunately stopped this practice in the mid-1940s, but instead stamped the reference number of the watch on the case back – either on the outside or inside. In that case, it is worth checking that the two or three digits below the reference number (which refers to the production number of that particular reference) is also stamped somewhere on the back of the lugs, as seen above.

Interesting Variations On The Flyback Mechanism

Now, before we move on to the development of the caliber 30CH, we want to digress slightly and mention two interesting prototypes created by Longines during the development of the flyback mechanism. Yes, while the 13ZN was officially the first flyback mechanism for mass production, there were at least two prototypes of the flyback mechanism prior to that. The first was based on the caliber 13.33Z (of which we just discussed) and the second was called the Caliber 15”’, which was based on the Valjoux 22GH mechanism.

The above two examples are both caliber 13.33Z equipped with the flyback function, as seen by the lack of a tooth on the reset lever. These were likely prototypes developed prior to the production of the caliber 13ZN, but it seems some examples were distributed to different retailers. There is a more in-depth discussion on the Italian forums here and here.

The Valjoux 22GH, on the other hand, has a more interesting story. Below is a clipping that shows the Longines Caliber 15".

First, it is interesting that Longines utilized Valjoux ebauches early on prior to the 1970s, at which point they began using the Valjoux ebauches as they were relatively cheaper than the in-house movements. Most of these Valjoux movements were monopushers, resembling the 13.33Z in functionality – as seen by the clipping above.

But a deeper look at the original patent, submitted for the flyback mechanism, yields a surprising observation.

Does the movement on the right look familiar? Yes – indeed, the mechanism displayed on the patent for the flyback mechanism was actually the Valjoux 22GH instead of the 13ZN that you might expect. But was there a Valjoux 15 with a flyback mechanism that was sold by Longines? Yes, there was.

Technically the title of first flyback chronograph mechanism should belong to the modified Valjoux 22GH instead of the 13ZN.

What does this mean? Technically the title of first flyback chronograph mechanism should belong to the modified Valjoux 22GH instead of the 13ZN. This is a fascinating topic that should probably be left to a another time.

The 13ZN movement was expensive to produce, especially when compared to the ebauches that other major brands had access to. During this period of time, Longines invested heavily in another round of research and development to produce a less costly version of the 13ZN, but still retaining the flyback functionality that was, at that time, unique to Longines. After producing the 13ZN for about 11 years, the 30CH was introduced in 1947.

Longines Caliber 30CH

The 30CH had the exact same functionality as the 13ZN. It had 17 jewels, a diameter of 29.80 mm and height of 6.20 mm, and beat at 18,000 vph. The movement was also typically installed with a shock-resisting ring, a part also found in most of the 13ZN-12 movements.

Similarly, notice that the reset lever does not have a tooth (circled in red). As the reset lever is engaged, the center chronograph wheel resets (red arrow). At the same time, the protrusion (circled in orange) pushes up the wheel that starts the chronograph (orange arrow), and subsequently lets it back down when the reset lever is released, restarting the chronograph function, producing a sequence of movements that allows for the flyback functionality.

The watches that come with the 30CH were designed to be "sportier" than the 13ZNs, reflecting the style of the times. Hence a larger number of the 30CHs can be found in steel, typically in waterproof cases and button pushers. Gold models of the 30CH can also be found in waterproof cases, a style not seen in the 13ZN.

The production of the 30CH (and its variants) spanned roughly 20 years, until the 1970s, when Longines was taken over by Ebauches S.A. and stopped in-house production of movements, instead opting to purchase ebauches from Valjoux S.A. This strategic decision unfortunately not only resulted in the extinction of a beautiful chronograph movement, but also ultimately proved futile in the face of the Quartz Crisis.

Variations

The 30CH family also had two other models, the L530 and L538. The L530 is essentially the same movement as the 30CH, but was cased in “dive” watches.

The design of this particular model was also the inspiration for the Longines Heritage Diver (L2.808.4.52.6), which added an hour counter and date display at 5 o’clock.

The final member of the family is the Caliber L538, which was a modified 30CH without the sub-seconds counter at 9 o’clock. This was also the last in-house chronograph movement designed by Longines. As the accuracy of the chronograph mechanism improved, the movement could now accurately time an event to one-tenth of a second (instead of the previously one-fifth).

Above is an infographic explaining how the Nonius system works.

At the same time, the 30CH movement also sometimes came without the flyback functionality. Notice the movement below, where there is a tooth on the reset lever, in comparison to a typical 30CH movement.

Once again, there is little information out there on why such a modification was made. If anyone has more information, feel free to add to the discussion.

Collectability

The watches that contain the 30CH caliber are in lesser demand than those with the 13ZN, both because of the longer production period as well as the slightly less "interesting" dial configurations. A good condition 30CH in steel, with a waterproof case and button pushers can be found anywhere between $5,000 and $8,000, with those in gold commanding a similar price. Some pristine examples with rare dials can reach the prices of 13ZNs as well. The diver (L530) and Nonius (L538) variations can also be found for similar prices, though those are arguably slightly rarer.

Final Words

The Longines 13ZN was one of the most technologically advanced and beautiful chronograph movements ever to be produced, even by today’s standards. It is one of the first truly in-house chronograph movements, which cemented Longines’ position as a premier brand back in the mid-20th century – and it is definitely an example to look out for in your collecting journey. In the future, if you do come by a vintage watch with "Longines" printed on the dial, take a second look – you might just find something very interesting.