The Definitive Guide: References Numbers All Collectors Should Know
You don’t need to know them all, but whether you are a seasoned watch collector or new to the game — these are the reference numbers all enthusiasts should know.
I remember my first day of work at The 1916 Company/The 1916 Company the way one remembers their first day of college. I am not sure what I wore, who I spoke to, what I did exactly, but the feelings are as ingrained in me as much as insider trading is ingrained in Congress.
By a stroke of luck my temporary desk was next to our Global Head of Sales and our Director of Originations. Between the two of them they put on a masterclass in reference number dialogue. Rarely ever calling a watch by the make or model they were able to have full conversations through reference numbers alone. It was wild to hear at first.
As someone who felt they were pretty knowledgeable about horology, its history and daily happenings, it was humbling as I felt beyond inadequate to stay in the conversation. But I sat and listened. I asked questions when I felt they weren’t overly stupid and found myself constantly googling every long string of numbers like John Nash in front of a chalkboard.
Eventually my desk moved, and the consistent banter I grew so accustomed to disappeared.
Those early conversations eventually became the basis for this article. As I scrambled to up my watch knowledge and strived for a Tim Mosso like recall — an impossible feat — I wanted to narrow down and to know…the reference numbers all collectors should have in their back pocket?
Beginning to understand reference numbers

Reference numbers are important in horology. Simply put, They are the best way to differentiate between specific models. Without them collectors would truly be lost at sea trying to separate the litany of Speedmasters.
Despite reference numbers’ initial intimidation, some brands such as Patek, have a true rhyme and reason for their numbers. Unlike some watchmaking counterparts that adhere strictly to a systematic numbering convention where each digit carries specific significance, Patek Philippe opts for a more flexible approach. While there is a discernible pattern, not every digit serves a predefined purpose, and the guidelines they follow may not always be absolute, which is essential to note for reference.
Patek Philippe’s numbering structure typically adheres to a general format, exemplified by sequences like 5726/1A-014. However, for simplicity, most individuals tend to refer to models by their initial four digits, which are often more memorable. Moreover, it’s common to observe that models within the same collection share the first two digits; for instance, the Calatrava line frequently commences with 52XX, while the Nautilus series typically begins with 57XX.

Nestled within the French-speaking region of Switzerland, Patek Philippe consequently, uses letters embedded within reference numbers and movement codes that are succinct abbreviations of French terms, a trait shared with Rolex.
These alphabetic characters within Patek Philippe’s reference numbers carry vital information regarding the watch’s case material. Referring back to the previous example (5726/1A-014), it becomes evident that this particular rendition of the Nautilus is crafted from stainless steel. The French for for steel is Acier, hence the A in the reference number.
If you see a J, the case material is yellow gold because the French word for yellow is Jaune. R is for pink gold because the french word for pink is Rose. You get the idea.
Heuer is another company that has put a system in place to understand its reference numbers.
Vintage Heuer watches utilized a four-digit reference numbering system. The first two digits denoted the caliber, the third digit represented the collection, and the fourth digit indicated the case metal.
For instance, the automatic Carrera 1158: “11” symbolized the automatic caliber 11, “5” denoted the Carrera collection, and “8” indicated a gold case. Additional letters could be appended to the suffix to specify the dial; for instance, the renowned 1158CHN featured a champagne dial with black (noir) subdials.
World renowned Heuer expert Jeff Stein has an incredible breakdown of the Heuer model/reference codes at his website OnTheDash.com
Similar to Heuer, numerous brands from that era devised numbering systems aimed at swiftly conveying information about the case material, caliber, and complications. Brands such as Universal Geneve, Omega, and Breitling adopted comparable systems. Occasionally, an extra character might be included after a period or a slash to convey supplementary details.
Unfortunately, there is no standardization across brands or for that matter even within some brands as some have changed their reference number structure and methodology over the years. It can be frustrating at first but when you put into perspective that many of these brands have been operating for 150+ years, I find it quite understandable.
Watch collectors often value certain reference numbers for their historical significance, design, innovation, or association with iconic timepieces or personalities.
The reference numbers all collectors should know.

Omega Speedmaster Professional – Reference 105.012, 105.003 and the 145.012

Venturing into the complex world of Omega Speedmaster reference numbers can be a daunting task. However, one notable exception is the iconic timepiece that made history by accompanying astronauts on the first lunar mission. The Omega Speedmaster 105.012, introduced in 1965, holds this distinction, having been worn by both Neil Armstrong and Edwin ‘Buzz’ Aldrin during the Apollo missions.
Interestingly,(according to legend) Armstrong left his 105.012 behind in the lunar module due to issues with the onboard clock. Buzz Aldrin later saw his speedmaster “disappear” while in transit to the Smithsonian.
In 1967, Omega released the 145.012, an upgraded successor featuring enhanced pusher construction and a distinctive single bevel case back. Despite the introduction of newer references, NASA continued to utilize the 105.003, due to existing stock. This explains why all three references were present on the moon between 1969 and 1972. Notably, the Speedmaster Professional 145.022, introduced in 1968, did not participate in lunar missions. Instead, it earned NASA qualification in 1978 for the Space Shuttle program, as indicated by the engraved text on its case back.
At the end of the day The two Speedmaster references all collectors should know are the ref. 105 and the ref. 145 due to their unmatched history and provenance, that catapulted the speedmaster into legendary status alongside the likes of the Submariner, Nautilus and Royal Oak.
Patek Philippe Nautilus – Reference 3700/1A and the 5711/1A (1976)

The Nautilus reference 3700/1A, introduced by Patek Philippe in 1976, marked a revolutionary step in luxury watchmaking. Designed by the legendary Gerald Genta, it redefined the concept of sports watches with its elegant yet robust stainless steel construction and distinctive porthole-inspired bezel. Initially met with skepticism, the 3700/1A eventually gained acclaim for its unconventional design. Equipped with Patek Philippe’s caliber 28-255C, this movement, a base JLC ref.920 is the granddaddy of all thin automatic movements and has been used by all of the Holy Trinity.
In 2006, Patek Philippe unveiled the successor to the revered 3700/1A, the Nautilus reference 5711/1A, during the watch’s 30th anniversary celebration. Maintaining the essence of its predecessor while incorporating modern updates, the 5711/1A retained the iconic octagonal bezel and integrated bracelet design that had become synonymous with the Nautilus line.
However, subtle enhancements such as a slimmer profile and refined dial layout brought a contemporary touch to the timeless silhouette. Powered by the self-winding caliber 324 S C, the 5711/1A offered enhanced precision and convenience, catering to the evolving tastes of discerning watch enthusiasts.
Since its introduction, the Nautilus 5711/1A has continued the legacy of its predecessor. Despite being initially overshadowed by the iconic status of the 3700/1A, the 5711/1A has emerged as a modern classic, sought after by collectors worldwide. With the limited edition run of Tiffany blue models and its recent phasing out, these two references are the cornerstones of modern Patek Philippe watchmaking.
Patek Philippe Perpetual Calendar Chronograph – Reference 1518 (1941)

Yes, another Patek, but still one we all should know. The Patek Philippe reference 1518 was introduced in 1941, it was the first perpetual calendar chronograph wristwatch ever produced in series by any watchmaker. The reference 1518 was a masterpiece of engineering. Ben Clymer said in a Reference Point article that “Not a single other manufacturer even attempted a perpetual calendar for another half century.”
At the heart of the reference 1518 beats the legendary caliber 13-130 Q, a manually wound movement. This movement not only powered the perpetual calendar function, capable of accurately tracking the date, day, month, and moon phases, but also featured a chronograph complication, allowing users to measure elapsed time with precision.
Despite being released over 80 years ago, the reference 1518 remains highly sought after by collectors. Its rarity, exquisite craftsmanship, and historical significance make it a prized possession for aficionados. Patek Philippe produced only a limited number of reference 1518 watches during its original production run, adding to its allure and exclusivity. Additionally, the reference 1518 set the standard for future Patek Philippe perpetual calendar chronographs, cementing its place in horological history.
While Patek Philippe no longer manufactures the reference 1518, its iconic status within the horological community stems from its pioneering design, technological innovation, and enduring appeal. For watch collectors, knowing the history of the reference 1518 is essential, as it represents a pivotal moment in the evolution of wristwatches and embodies the pinnacle of craftsmanship and luxury.
Audemars Piguet Royal Oak – Reference 5402ST (1972)

The Audemars Piguet Royal Oak Reference 5402ST, launched in 1972, is celebrated for its groundbreaking design that defied traditional watchmaking norms. Another watch famously designed by Gerald Genta, the Royal Oak was named after the iconic British Royal Navy battleships, signifying its maritime provenance. One of its most striking features is the octagonal bezel with exposed screws, inspired by the portholes of naval vessels. This design element not only served as a visual homage to nautical aesthetics but also provided structural integrity to the watch.
The Royal Oak Reference 5402ST featured an integrated bracelet seamlessly integrated into the case, a departure from the prevailing trend of attaching straps to lugs. This integration not only enhanced the watch’s overall aesthetics but also contributed to its durability and comfort on the wrist. The bracelet’s design, characterized by its unique combination of polished and brushed surfaces, further accentuated the Royal Oak’s sporty yet sophisticated appeal.
Additionally, the Royal Oak Reference 5402ST boasted some new finishing touches, such as the “Grande Tapisserie” pattern on its dial. This textured pattern, along with the applied hour markers and luminous hands, ensured optimal legibility. At 39mm and with a seemingly impossible thickness of 7mm, this size was only made possible by the Jaeger-LeCoultre Cal. 920 movement aka the ref. 2121. The cal. 920 is a legendary caliber that all collectors and enthusiasts should know as well.
The Royal Oak Reference 5402ST’s bold design challenged conventional perceptions of luxury watches, as it was the first high-end timepiece crafted from stainless steel. At a time when precious metals like gold dominated the luxury watch market, Audemars Piguet’s decision to use stainless steel was revolutionary. This move not only democratized luxury watchmaking but also appealed to a younger, more adventurous clientele.
What makes this reference memorable is simply that it is the first Royal Oak. This doesn’t mean that all “firsts” should be remembered, but for Audemars Piguet, a company that has turned somewhat into a monobrand, this is the one to know.
IWC Portugieser – Reference 325 (1939)

The IWC Portugieser Reference 325, originating in 1939, represents a significant milestone in the history of horology. Conceived during an era dominated by smaller, traditionally styled wristwatches, the Portugieser Reference 325 stood out with its oversized case and minimalist aesthetic. This distinctive design was born out of a special request from two Portuguese businessmen seeking a wristwatch with the precision of a marine chronometer.
The defining feature of the Portugieser Reference 325 is its large and clean dial, characterized by Arabic numerals, leaf-shaped hands, and a railway track minute scale, offering exceptional legibility and sophistication. This emphasis on readability and simplicity underscored IWC’s commitment to functionality and precision, making it an ideal timepiece for navigational purposes.
Underneath its elegant exterior, the Portugieser Reference 325 housed the Caliber 74 movement, a high-quality pocket watch movement modified to fit the larger case. Its manual winding mechanism and robust construction reflected IWC’s dedication to craftsmanship and innovation.
This reference is important because it is essentially the first “oversized” wrist watch ever produced. At 40.5mm it towered over the diminutive contemporaries that rarely ever broke the 35mm mark.
Another interesting anecdote about the story of the ref. 325 is that it wasn’t always called the 325. Arthur Tuchot of Phillips once described this ref as “The anonymous watch that became world famous.”
The IWC website gives some more insight to this tale. “That watch, though, initially did not have a name, nor even a reference number. A review of case numbers in IWC’s records only revealed a denomination for the case model: “Mod. 228”. Some early examples of this wristwatch had this number 228 engraved on the inside case back.
IWC’s administration must have equally confused by this case number designation without a reference number. Consequently, someone at the manufacture started using the term that would become later highly noted: “Reference 325”. It is this number which designates the model of the original “Portuguese” wristwatch, even though that model was never shown in any IWC catalog.”
Despite its modest reception upon its release, the Portugieser Reference 325 has since earned iconic status within the horological community. For watch connoisseurs, understanding the history of the IWC Portugieser Reference 325 is essential, as it represents a pivotal moment in the evolution of wristwatch design.
Breitling Navitimer – Reference 806 (1954)

The Breitling Navitimer Reference 806, launched in 1954, holds a revered status as an aviation icon and a symbol of precision engineering. Designed specifically for pilots and navigators, the Navitimer quickly became synonymous with the golden age of aviation, thanks to its innovative slide-rule bezel that allowed pilots to perform complex calculations essential for flight navigation directly on their wrist.
The Navitimer Reference 806 boasts a distinctive and functional design, characterized by its large, legible dial, prominent slide-rule bezel, and chronograph subdials. This combination of form and function not only facilitated accurate timekeeping but also enabled pilots to perform a wide range of essential calculations, including fuel consumption, airspeed, and rate of climb, making it an indispensable tool for aviation professionals.
At its core, the Navitimer Reference 806 housed the Venus 178 manual-wind movement, renowned for its robustness and accuracy. This movement ensured that the 806 could withstand the rigors of aviation and deliver precise timekeeping under any circumstances.
If we are being serious it is the panda version of this watch that we all know and love. I hate to use the word iconic too often as not every memorable watch or historically significant watch is actually iconic, but The Navitimer is just that. It is recognizable by those outside of the watch community and it has been used by people from penthouses in the sky to construction workers on the ground.
Over the years, the Navitimer has evolved into one of Breitling’s most iconic and beloved collections.
Tag Heuer Monaco – Reference 1133 (1969)

The Tag Heuer Monaco Reference 1133, launched in 1969, is an iconic timepiece celebrated for its groundbreaking design and association with motorsports. Designed by Jack Heuer, the Monaco broke new ground as one of the world’s first automatic chronograph watches, featuring a bold and distinctive square case that defied conventional watch design norms.
The Monaco Reference 1133 boasts a striking and avant-garde design, characterized by its square stainless steel case, contrasting subdials, and bold red accents. This bold aesthetic not only captured the spirit of the 1960s but also reflected Tag Heuer’s innovative approach to watchmaking. The Monaco’s unconventional design quickly made it a favorite among racing enthusiasts and celebrities, cementing its status as a cultural icon.
Powered by the Caliber 11 automatic movement, the Monaco Reference 1133 offered cutting-edge chronograph functionality with its innovative modular construction. This groundbreaking movement, developed in collaboration with Breitling, Hamilton, and Dubois Dépraz, marked a significant milestone in the history of watchmaking, paving the way for future generations of automatic chronograph watches.
The Monaco Reference 1133’s enduring appeal among collectors and enthusiasts can be attributed to its revolutionary design, technical innovation, and association with motorsports legends such as Steve McQueen, who famously wore the Monaco in the 1971 film “Le Mans.” Over the years, the Monaco has evolved into one of Tag Heuer’s most iconic and sought-after collections.
Cartier Tank – Normale (1919) — The Watch Without a Reference #

When trying to decide the reference numbers that all collectors should know I essentially brainstormed all of the cornerstone brands and models that make up the foundation of our modern watch world. It is hard to talk about the current horological landscape without discussing the impact and influence of a Speedy, Nautilus, and Navitimer.
Another watch that is a foundational model is the Cartier Tank, specifically the Normale. At first I was finding varied reference numbers for what would be considered the inaugural run in 1919. And before the talking heads of the internet correct me and say 1917 — according to Cartier archives the first was sold in 1919 and the story about General Pershing receiving one in 1917 is a (potential) urban legend.
That said, I was surprised to find out the Tank had no reference number and moreover there was no clear date as to when Cartier began adopting a structured reference number system. Despite there being no actual reference number I still thought including this model was just as important to the story.
The Tank is iconic. It is the Cartier Tank, everyone remotely interested in watches knows this model. But the first one is arguably the most important one.
The Cartier Tank, was introduced in 1919 by Louis Cartier. Inspired by the design of Renault tanks used during World War I, the Tank revolutionized watchmaking with its distinct rectangular case and bold geometric lines. Louis Cartier, known for his avant-garde approach to design, sought to create a timepiece that would embody both strength and sophistication, and the Tank was the embodiment of this vision.
The Tank is technically not the first watch to be worn on the wrist but the first designed to be worn on the wrist, and also designed with aviation in mind. This was arguably the birth of the tool watch, and for it to come from such an esteemed maison such as Cartier makes it even more special.
Referring Back
The significance of knowing reference numbers as a benchmark of an educated collector is a topic of ongoing debate. Personally, I don’t take a strict stance on this issue. While I believe it’s essential to have a willingness to learn and familiarize yourself with some reference numbers, even if you are part of the 3% of the global population with dyscalculia, I don’t think it’s a definitive measure of a collector’s sophistication. As collectors mature and gain experience, they will naturally commit reference numbers to memory. However, being able to recite them effortlessly doesn’t necessarily make one collector more refined or knowledgeable than another.