In our modern digitalized world famous for the “internet of everything”, it’s easy to forget that analog tools and their functions in the decades before computers were actually the norm. Today, most people can pick up a tool or instrument from the past and have no idea what it is or how it would even work.
Heck, try even explaining what a “VHS” tape is to my 5-year-old niece and why we’d have to drive to the local Blockbuster down the road to rent one every Friday night in the 1990s instead of just switching on Netflix (how “20th Century” of us).
Even watches overall are “outdated tech”; need the time? Simply look at the corner of your computer screen, or pull out your iPhone to quickly check. But what do you do if your battery dies or you forget your phone at home?
I’m not suggesting that everyone has multiple analog redundancies for every part of their waking lives; however, simple things like wristwatches can function as totems, expressions of our aesthetic sense and tastes, and nostalgic reminders of when things weren’t so digital.
About the Slide Rule Complication
On the topic of watches (that’s why you’re here after all, right?), it can be said with certainty that every function and complication developed came out of a specific real-world use or need. Take, for example, the dive bezel, used to track the elapsed time on a dive to ensure the user isn’t subject to decompression sickness.
Or the GMT hand, developed specifically for pilots frequently traveling across time zones. But perhaps the most visually impactful, with functions not limited to one specific purpose, is the sliding rule complication (or slide rule bezel).
Developed by Breitling in the 1950s at the request of the Aircraft Owners and Pilots Association (AOPA), the sliding rule bezel was applied on the now iconic Navitimer (“navigation timer”) model to aid pilots in navigation and perform complicated arithmetic with a simple twist of the bezel.
This feature was a hit, and the concept has been adopted by many watch companies in the decades since, even as its practical use has fallen out of favor with the advancement of computers and technology.
What Is The Purpose of Slide Rule Watches?
While the modern buyer or watch enthusiast may no longer rely on slide rule bezels to fly planes or perform complicated arithmetic, this doesn’t detract from the bezel’s functionality. The tool is still there; the user just has to learn to use it!
So even if you purchase a watch with a slide rule bezel for the looks alone or appreciation for its use in history, here are a few ways you can get some use out of that Navitimer (or any of the other options we’re about to list below).
First, some basics:
There are two scales and unit index markers; the inner scale, running along the outermost perimeter of the dial itself, and the outer scale, running along the periphery of the bezel itself. The index markers (specifically on a Navitimer; this may vary on other models) are indicated in red and serve as a reference point in the alignment of the rule.
The bezel can be moved in either a clockwise or a counterclockwise direction. Finally, the slide rule doesn’t consider decimals; finding the number closest to the one you want, regardless of the decimal point sits, will be the way to go.
Example: “50” on the slide would equate to 5 as input; Or, if the answer reads as 32.5, and we know intuitively the number should be in the hundreds, we’d read it as 325 instead.
Let’s say we want to multiply 9 times 12. To do so, align the unit index 10 on the outer scale to the 9 on the inner scale. The scale is now aligned to all multiplications of 9. From here, find 12 (the number we’re multiplying against 9) on the outer scale, and the answer displays as 10.8, which, intuitively, we know to read as 108. Note: Multiply your restaurant bill by 20, and you’ll get an approximate tip figure to impress your friends with
Let’s try division! For 20 divided by 16, move 16 on the outer scale to 20 on the inner scale. Our answer is read from the outer unit index 10: “12.5”, which, intuitively, we know would convert to 1.25.
Knowing that speed equals distance divided by time, we can calculate the average travel speed by looking at the inner scale value corresponding to 10 on our outer scale.
If we know it took us three minutes to pass one landmark from the start of our journey, we’d see that the inner scale reads about 33.5, or 3.35 miles per minute. On to the watches!
The Best Slide Rule Watches
1. Casio Edifice (ref. EF-527D-1AVEF)
Measuring 45mm in diameter, 50mm lug-to-lug, and 11mm thick, the EF-527D is an affordable and reliable step into the slide rule watch pool for anyone wanting to test the sizing or look of such watches.
Capturing the toolish busy look and functionality of watches at multiples in price, this model Edifice benefits in its quartz movement with a svelte case, screw-down crown, and 100 meters of water resistance despite also being a chronograph.
This combination of chronograph functions in mechanical watches typically results in a lower water resistance rating (30-50 meters in most cases), making the EF-527D an attractive alternative in both the practical sense and for the wallet.
Retail Price: $190
2. Citizen Promaster Nighthawk Eco-Drive (ref. BJ7006-56L)
Anecdotally, for every Breitling Navitimer I’ve seen on a pilot’s wrist when flying, I’ve seen at least 3x the amount of Citizen Promaster Nighthawks on their wrist instead (filtering out all Apple Watches, naturally). Point being, if it’s good enough for a large number of real actual pilots, it should be good for us normie passengers as well. With a pleasant 42.4mm case diameter, 12.7mm thickness, and 46.5mm lug-to-lug, it’s also quite wearable for a pilot’s watch, which is typically large in size for practical visibility in the cockpit.
Add in 200m of water resistance and the hassle-proof light-powered Eco-Drive movement, and it’s no wonder that so many choose the Nighthawk when looking for a practical and reliable watch. The BJ7006-56L, in particular, is styled in an attractive blue and yellow in honor of the US Navy’s elite flight demonstration squadron, The Blue Angels.
Retail Price: $475
3. Seiko Prospex SRPB57J1
The SRPB57J1 is Made in Japan as part of the Seiko “Sky” collection, within the Prospex (“Professional Specifications”) line of watches intended for use by professionals. Powered by the caliber 4R35 movement, the watch is an automatic mechanical movement with both hand winding and hacking seconds (i.e.: the seconds hand stops when the crown is pulled out for a more precise time setting) and is rated to 100m of water resistance.
Without chronograph functionality, as we typically see in slide rule bezel watches, the SRPB57J1 offers a clean dial aesthetic in a 44.7mm diameter case with 12mm thickness. If you’re looking for an affordable mechanical watch alternative to the Pilot’s watch style, this Seiko is a great option.
Retail Price: $497
4. Hamilton Khaki Aviation X-Wind (ref. H77912135)
Hamilton has a long history of aviation watches (even providing the US Airmail service with watches as of 1918) and has developed the Khaki Aviation line in conjunction with air squadrons and renowned pilots to create function-forward timepieces that can be used effectively on the job.
In the X-Wind (ref. H77912135) in particular, we have a combination of crosswind calculator, chronograph, and GMT functionality, all packed within a 46mm diameter case with 14mm thickness and a caliber G10.962 ETA Quartz movement accurate to +/- 10 seconds, water resistant to 100m to boot. It’s harder to imagine a more useful set of complications for a Pilot’s watch; just don’t ask us how to calculate crosswinds (we’ll defer to the watch manual book for that).
Retail Price: $1,045
5. Seiko Flightmaster SNA411
In the pantheon of household name Seiko watches, the SNA411 Flightmaster (colloquially known as the “Flighty” in some circles) is the watch of choice in the pilot watch category. Its overall popularity is attributed to a few things: its wearability, looks, and function.
With a 42mm diameter case, 13mm case thickness, and short lug-to-lug of 44mm, the Flightmaster can be worn on a large range of wrist sizes, with its good looks and comfort accentuated by the infinite combination of straps and watch bands (21mm lug width) it can be placed on.
The reliable Seiko caliber 7T62 quartz movement, screw-down crown, 200 meters of water resistance, and alarm flyback chronograph capability are all the icing on the cake for this classic fan favorite.
Retail Price: $475
6. Hamilton Khaki X-Patrol (ref. H76566751)
Returning to the Hamilton Khaki Aviation line of watches, we have the 42mm diameter (16mm thickness and 52mm lug-to-lug), automatic mechanical caliber H-21 movement X-Patrol, reference H76566751, with 60 hours of power reserve.
A looker of a watch accentuated with a see-through case back to view the movement, the X-Patrol is rated to 100m of water resistance, no small feat for a mechanical chronograph which also features an inner rotating bezel in place of the typical slide rule bezels exposed on the outside of the case. With a day and date function windowed on the right-hand side of the dial, the additional sub dials are positioned at 12, 6, and 9 in an attractive configuration.
Retail Price: $1,695
7. Ollech & Wajs Zürich OW P-104
Founded in the city of Zurich in 1956 by business partners Joseph Ollech and Albert Wajs, Ollech & Wajs was formed to create robust, legible, and reliable tool watches powered by proven movements of the day; a brand ethos that still continues through today.
The P-104 in question is not a re-issue of a historic watch but rather a re-imagination of the watches created throughout the brand’s history. Measuring in a widely accessible 39mm diameter case, 50mm lug-to-lug, and 12.5mm in thickness, the P-104 has a fully brushed case which speaks to the robustness intended in use.
Of note, this is not a chronograph watch, but one built with both the military and commercial pilots in mind featuring a slide rule bezel akin to a diver’s bezel in form. With the proven workhorse ETA 2824-2 automatic mechanical movement inside and a 300m water resistance, Ollech & Wajs have created a particularly unique watch stylistically and function-wise for discerning collectors.
Retail Price: $1,250
8. Victorinox Airboss Mach 9 (ref. 241710)
Outside of the Swiss Army Knife collector community, luggage, and cutlery worlds, Victorinox also makes some of the most rugged and capable wristwatches available on the market. Enter the Airboss Mach 9, reference 241710; 45mm in diameter, 15mm thick, with uncharacteristic left-sided “destro” crown and chronograph pushers, and slide rule accessible via a crown at the 2 o’clock position.
The Airboss Mach 9 is a sizable and unique watch for those looking to make a statement, with 100m water resistance, chronograph, and automatic mechanical Valjoux caliber 7750 movement to boot. Even cooler, Air Force One squadron models have been known to surface on the aftermarket as well.
Retail Price: $2,450
9. Hamilton Khaki Aviation Converter Auto Chrono (ref. H76726530)
Launched in 2020, the Khaki Aviation Converter Collection from Hamilton aims to capture the essence of traditional “E6B” flight computer-style watches, similar to the Navitimers of the world, which are the usual suspects in the genre.
It must be noted that the reference H76726530 is not a re-edition, though slide rule bezels have existed on previous Hamilton models in the past (look no further than this list). Rather its classic styling speaks to the success Hamilton achieved in capturing that vibe in modern materials and execution.
Measuring 44mm in diameter and about 15mm in thickness, the Auto Chrono wears with a presence on the wrist with polished chronograph pushers and lug bevels, adding an additional layer of quality. With a 100m water resistance rating and the anti-magnetic silicon hairspring of the caliber H-21-Si movement, Hamilton has created a new riff on a classic design with all the advancements of modern watchmaking tech.
Retail Price: $1,995
10. Zeno-Watch OS Slide Rule Chronograph (ref. 8557CALTH-a1)
With a 47.5mm case diameter, Zeno-Watch classifies the Slide Rule Chronograph reference 8557CALTH-a1 within its Oversized “OS” collection, and rightfully so. Powered by an automatic chronograph Valjoux 7750 (with approximately 42 hours of power reserve) and rated to 30m of water resistance, the watch is certainly a bold look.
Coupled with a crown at the 10 o’clock position to actuate the inner rotating slide rule, despite its size Zeno-Watch provides a clean and attractive aesthetic, balancing bold lumed Arabic along the dial with attractive cathedral-style hands.
Retail Price: CHF 2,538
11. Oris Big Crown X1 Calculator (ref. 01 675 7648 4264-Set 5 23 77)
Originally developed as an homage to the first manned supersonic flight of October 14th, 1947, the Oris Big Crown Calculator is a uniquely gray-plated (PVD) stainless steel automatic chronograph from the brand.
Clocking in at 46mm in diameter and 16mm in thickness with a 23mm lug width, the watch will certainly have a presence on the wrist. Still, with its grey PVD coloring and bold Arabic at 12, 3, 6, and 9 with the utmost in legible hands, you can’t knock the legibility and function of this uniquely styled slide rule watch. Particularly attractive is the coin edge bezel, a call back to vintage styling despite its outwardly modern case finish.
Retail Price: $3,950
12. Breitling Navitimer Automatic 41 (ref. A17326241B1P1)
Redesigning and creating line extensions of classic, well-known watches can often be a delicate subject. Get it wrong, and the legions of fans will let it be known. Do it right, and you might just capture something new, worthy of its own praise.
When Breitling sought to refine the Navitimer in the Automatic 41, it can’t be denied that the clean dial aesthetic lacking chronograph subdials and functionality captures the essence of the Navitimer at its core, providing a clean and direct focus on the bi-directional slide rule bezel overall.
With a 10.10mm thickness and 47.9mm lug-to-lug, the classed-up Automatic 41 will wear closer to a dress watch than the tool watch feel of the Navitimer Chronograph it pulls inspiration from. Available on a number of leather straps, the Automatic 41 is truly elegant.
Retail Price: $4,750
13. Sinn 903 ST Navigation Chronograph
Like many brands of the Swiss watch industry in the 1970s, Breitling was hit particularly hard by the quartz crisis, eventually closing its doors in 1979. In the wake of staff layoffs and liquidation, the rights to the Navitimer were sold to Sinn and Sicura, with Sinn, in particular, purchasing the rights to the Breitling 806 and 809 Navitimer models of the day.
Sicura continued to manufacture watches under the Breitling name (as well as owning the “Navitimer” name outright), while Sinn continued to develop the Navitimer technology into present day. The 903 ST Navigation Chronograph is an attractive culmination of those decades since, featuring a La Joux-Perret 8000 column wheel chronograph movement in a wearable 41mm diameter case (14.5mm thick, 48.5mm lug-to-lug) with 100m water resistance.
For anyone looking for an alternative to the Breitling Navitimer, the Sinn 903 ST is a surefire choice, both with its historic ties to the Navitimer itself and the classic telltale design at nearly half the price.
Retail Price: $3,580
14. Breitling Navitimer B01 Chronograph (ref. AB0137211B1P1)
The icon itself. When we talk about slide rule complicated watches, the Breitling Navitimer B01 Chronograph is most certainly the standard to which all others are judged. From its initial inception in 1952, partnering with the Aircraft Owners and Pilots Association (AOPA) in developing a tool allowing pilots to perform all necessary flight calculations, to the latest iteration over 70 years later, the Navitimer defines the pilot chronograph genre.
Of design note, the updated dial revives the AOPA wing logo to its original position at 12 o’clock, with new color variants in green, copper, and blue now available. The caliber Breitling 01 movement (70-hour power reserve) is housed in the familiar 46mm diameter case with 13.95mm thickness and is rated to 30m of water resistance. In a world of options, if you’re looking for the original archetype, there is no other choice.
Retail Price: $9,200
15. Richard Mille RM 039
It’s always fun to have a halo piece, and with the million-dollar RM 039, that’s a really high halo. But if your pockets are particularly well lined, and you have all the right connections to get it (limited to 30 pieces), the RM 039 offers one of the most difficult and complex Richard Mille watches to buy, with nearly 1,000 individual parts comprising its 50mm diameter case (at 19.4mm thick).
With an oversized date display, adjustable UTC function for displaying a second time zone, gearbox-like function selector (winding, neutral, hand0setting, UTC setting functions), power reserve indicator, bidirectional slide rule bezel, and oh, by the way, did we mention that it’s a tourbillon; we have one heck of a watch constructed and finished to a degree simply impossible at a lower price point. How much is it again?
Retail Price: €1,042,500 (As they say, “If you have to ask…”)
The slide rule complication can seem like an anachronism, an analog function from another age when computers and digital technology weren’t even yet a dream. And yet, wristwatches with slide rule complications continue to be made in the modern era.
Whether as a nod to history or an aesthetic appeal to aviation-age romance, the 21st-century watch collector can still find modern applications to this anachronistic tool. Just be sure to charge your phone the next time you forget your watch!