The Unsolved Mystery of the Chronograph Hash Marks


The Unsolved Mystery of the Chronograph Hash Marks


This exploration of the case of the curious chronograph hash marks was contributed by Revolution Community member Achim Ruehlemann, whose first loves are watches, wine, vintage cars, tennis, skiing and his family.

Let’s say you’ve recently bought a brand new chronograph. You look down at your wrist with with pride, ready to conquer the world, when you notice these strange lines in the minute counter at the 3-, 6- and 9-minute marks. You thought you did your research and knew everything there is to know about your precious timepiece, but you are stumped. What do these strange lines mean; who came up with them; and why are they on your watch?

Granted, not all chronographs have this odd distinction, so don’t feel bad if you’ve never noticed them before. Most modern chronographs have conventional 30-minute counters, highlighting each five-minute mark with a bolder or elongated hashmark. However, in our world of endless homage releases and vintage-inspired timepieces, one will find numerous examples of these in the wild, such as the Blancpain Air Command and the Longines Avigation Big Eye, among others.

Blancpain Air Command Flyback Chronograph

Longines Avigation BigEye

Then there are some examples of even more exotic timepieces out there that abandon the five-minute intervals altogether and go straight to a 15-minute counter, sub-divided in three-minute increments, such as the Breitling AVI 765 re-edition and the subsequently released Super AVI series. There’s something going on here. Further adding to the mystery is the fact that watch brands, such as Universal Geneve incorporated the three-, six- and nine-minute demarcations as early as the 1930s. What was the rationale behind this uncommon dial design?

Universal Genève Tri-Compax

Let’s take a closer look and go back in time to find out what’s behind this mystery, specifically to the pre-digital age, a time before cell phones, Netflix, and self-driving cars. One explanation that had been swirling around the Internet and one of the most plausible theories, was that the three-minute increments of the 30-minute chrono sub-dial were there to time international calls or pay phone calls. It is, in fact, true that during the mid-century telephone rates would change and increase in three-minute intervals. As such, it would make sense to be aware of the rate hike after the initial 180 seconds.

Just imagine; it’s the mid seventies, you have one phone in the house, and it’s a rotary phone that you have to share with everyone — how did we ever survive? — and making a phone call is expensive, very expensive, especially long distance and in particular calling overseas. Remember, we are not in the WhatsApp age, yet. And here is the kicker: your summer crush, that Swedish au pair you love so much, had to go back home and the only way to stay in touch with her is to call her under the watchful eyes of your father with his trusty chronograph.

Montblanc Heritage Pulsograph Limited Edition 100

Now that we have a possible explanation for these mysterious three-minute hash marks, one can’t help but wonder why it had primarily been pilot watches that incorporated the three-minute sub-division and/or the 15-minute counter. Do pilots just spend too much time on the phone and need to be reminded when to hang up?

One can’t really imagine that the esteemed engineers at aviation-inspired manufacturers, such as Blancpain, Breitling, Longines and others would have condoned such a nuisance application for an otherwise meticulously crafted Swiss timepiece. It is further interesting to note that in the mid 50s, Breguet would produce watches exclusively for military Air Force units specifically using three-minute increments on a 30-minute or 15-minute totalizer. For one possible explanation, think Indy. Indiana Jones.

Imagine Indy being chased, trying to get away in his little beat-up bi-plane, having somehow to figure out if he has enough speed to lift off without getting shot or falling off the cliff. Here, his chronograph comes to the rescue! Indy knows that he can use a simple calculation to determine his fate, using the mighty ‘Rule of three’ and his trusted old timepiece with those funky hash marks.

Three-minute as well as six-minute increments can be used to quickly calculate rates, such as distance and speed, as three minutes is exactly 1/20 of an hour and six is 1/10 of an hour. Therefore, they are much easier to work with than five-minute or 10-minute increments, which would equate to 1/12 of an hour or 1/6 of an hour respectively.

Since Indy’s speedometer is blown to bits, he needs to figure out his pace by quickly calculating the distance in yards his plane travels in three minutes, which is about equal to the speed in knots divided by 100. Let’s assume he travels one mile per minute, equaling three miles over three minutes, totaling 5,280 yards, which in turn equates to 52.8 knots. Oh dear, that won’t do it, he needs to get to 60 knots to take off. But lo and behold, Indy comes through, and he escapes into the sunset.

These types of “on the fly” calculations could be lifesaving for pilots at a time when the use of electronics was scarce, and time was of the essence. So, it would make sense to imagine that the three-minute increments had purposefully been applied to the minute chronograph counter for that exact reason.

The last theory on this subject is that the 15-minute versus the more conventional 30-minute sub-dial was intended for aviators to time their final plane check before taking off — but that just sounds a bit too simple.

40mm Breitling Navitimer Pilot's Chronograph ref. 806, Circa 1950s (©Revolution)

What can we conclude from this? The next time you are thinking about purchasing a vintage or re-issued chronograph, take a closer look at the sub-register and see about those hash marks. Whichever theory you choose to accept is up to you. They all make sense in their own way, and while none are based on scientific evidence or documented archival footage, if anyone asks you about those funky three minute lines or that odd 15-minute sub-dial, just be sure to make it a good story.