The concept and evolution of watches as seen through the operating system: Bezel

The rotating bezel is an essential feature of diver's watches. Why did most diver's watches adopt the unidirectional rotating bezels we see today? What are the uses of rotating bezels in other watch genres? A cutting-edge writer with a science background explains.

　When a user uses a wristwatch to measure time, it would be ideal if they could remember the start time of the measurement, but there is a risk of remembering the start time incorrectly or misreading the elapsed time. So how can we measure elapsed time using the hour and minute hands that continue to move as time passes? From this perspective, the "rotating bezel" was proposed, which makes the bezel movable so that the starting point of the scale can be adjusted to a position that is convenient for the user.

　The early diver's watches used rotating bezels instead of chronographs to measure time while diving, and this later became the standard. Starting from this, we will examine the advantages and convenience of rotating bezels.

Do you move the hands or the scale to measure time?

　According to the JIS standard (JIS Z 8103:2019), measurement is defined as "the process of experimentally obtaining the value of a quantity by comparing it with a unit of measurement of the same type of quantity." Looking at the "measurement of elapsed time" with a clock from this perspective, we can see it as converting the invisible passage of time into a "quantity" by the angle of the movement of the hands, and then "measuring" it by comparing it with the scale, which is a "unit of measurement" that corresponds to the angle.

　Here, a chronograph is a device that starts the hands at any time to measure elapsed time, and can be interpreted as a function that allows the user to manipulate the angle at which the hands move to suit their needs.

　So, instead of hands, we can imagine a mechanism that operates the "scale," another element essential for measuring time. Yes, this is the rotating bezel. Rotating bezels have a history that dates back to the dawn of diver's watches, and they have a very deep connection.

　This begs the question: "Why did the early diver's watches have rotating bezels instead of chronographs?" Let's start our discussion with this question.

Advantages of a Rotating Bezel Over a Chronograph

　Chronographs allow you to start the hands at any time, and many models can measure time with an accuracy of better than one-fifth of a second. The advantage is that they can measure time accurately down to the second, which has made them a major player in sports, science and technology, and the military, where this is required. However, they are not versatile. Disadvantages include the fact that measuring down to the minute is less legible than measuring down to the second, and the need for additional controls for starting and stopping.

　So what kind of watch would be best suited to measuring minutes or hours (i.e., no need to measure to the second) and not have any additional controls, like chronograph pushers, that could puncture the case and compromise its airtightness? I believe that was the early diver's watch.

　Users use a diver's watch to measure their remaining dive time, which is calculated from the capacity of their air tank. Today, the maximum dive time from an air tank is roughly 40 minutes, so a diver's watch is required to measure time of around 30 minutes with good legibility. Furthermore, in the early days of diver's watches, it was difficult to provide pushers that could be operated when needed while still maintaining water resistance. Therefore, it's easy to imagine that a method of measuring time that didn't compromise the airtightness of the case was desirable.

　Finally, three-hand movements were the only option for reliable automatic winding. Since trouble with a diver's watch can literally be a matter of life and death, any operation that could potentially lead to a breakdown was to be avoided. Therefore, operating the crown while manually winding the watch was a risk that could allow moisture to seep in. It wasn't until 1969 that automatic chronographs were introduced, and in the early days of diver's watches, it was natural for divers to forgo the chronograph and opt for a three-hand movement if they wanted an automatic.

　From the above, it can be said that the rotating bezel, which measures time by moving a scale, was suitable for early diver's watches when it was difficult to adopt chronograph movements. The advantages of the rotating bezel for diver's watches are clear when we consider the history so far.

-Excellent visibility for measurements in minutes (hours for the hour hand)
-Does not affect the waterproof performance of the case
-Time can be measured with a three-hand movement

　One watch that took advantage of these advantages and adopted a rotating bezel to set the tone for modern diver's watches was the Blancpain Fifty Fathoms, first released in 53. Its developer, Blancpain's CEO at the time, Jean-Jacques Pfister, had an experience where he forgot his dive time while diving in France and nearly got lost, so he incorporated a function that allowed the dive time to be displayed at a glance into the Fifty Fathoms.

　Let's review how to use a rotating bezel for a diver's watch. The movable bezel is attached to the outer periphery of the dial and has a scale that is independent of the dial's display. By rotating the bezel, the zero position of the bezel can be set to any position, and the scale can be used for various measurements. Specifically, to measure dive time in minutes, align the zero position of the bezel with the direction of the minute hand at the start of a dive. The bezel of a diver's watch has a minute index, allowing you to see at a glance how far the minute hand has advanced from the zero position.

　The key point is that the Fifty Fathoms was equipped with a locking mechanism for its movable bezel. Suppose the bezel were to unintentionally move clockwise while measuring remaining dive time. This would result in the bezel moving in a direction that would incorrectly read the remaining dive time as longer, which could be dangerous as it could lead to a shortage of air in the tank. To prevent such accidents, Jean-Jacques Pfister equipped the Fifty Fathoms with a locking mechanism that would prevent the bezel from rotating unless it was pressed in. This was an idea that only someone like him, who actually divers, could have come up with.

Unidirectional rotating bezels have become mainstream

　After the introduction of the Fifty Fathoms, diver's watches continued to evolve through the dedicated development of various manufacturers, and the requirements for such watches were compiled into ISO 6425 in 82. This standard required that watches be equipped with a rotating bezel or an equivalent time measurement function, and that it be prevented from malfunctioning, demonstrating the importance of a rotating bezel and a mechanism to prevent unintentional bezel rotation when diving. However, the push-in locking mechanism used in the original Fifty Fathoms remained in the minority, and unidirectional rotating bezels became the norm.

　A unidirectional rotating bezel uses a spring element to press a pawl into a gear-shaped recess on the inside of the bezel, allowing the bezel to rotate counterclockwise by pushing the pawl aside, but clockwise rotation prevents the pawl from getting caught and locks the bezel. This is the same principle as the locking mechanism found in the manual winding mechanism of a watch movement.

　This structure allows the unidirectional rotating bezel to be set to any position without the need for special operations, while preventing the bezel from accidentally rotating to the right, which could be dangerous, as shown in the previous example. Its simple structure, high reliability, and easy maintenance also contributed to its widespread popularity.

　The simplest way to create a unidirectional rotation prevention mechanism is with a leaf spring and a recess inside the bezel, but it has been continuously improved to improve durability and operability. Among these, Damascus has an elaborate structure.

　While many bezels are secured by a press fit, Damascus diver's watches use a C-ring to secure the bezel. They also feature a ceramic ball bearing to ensure stable movement of the bezel, and a ceramic stopper that hooks into a recess on the bezel, creating a clicking sensation without the use of a leaf spring. Because it's made of ceramic, it has excellent wear resistance and a long lifespan.

　Furthermore, an O-ring is provided to prevent dust from getting inside the bezel, preventing performance degradation and improving maintenance. This structure results in a smooth operation with no rattle, a crisp, rounded but clear click, and excellent quietness, which can be enjoyed even during normal use.

A push-type unlocking mechanism to prevent trouble caused by the watch

　While unidirectional rotating bezels have become the mainstream for bezels with malfunction prevention features, the push-in rotating bezel has also been carried over to the Sinn "T1 (EZM14)." The T1 is a model with a titanium case and high water resistance of 100 bar. While Sinn offers many high-performance diver's watches such as the UX (EZM2B) with a water resistance of 500 bar, the T1 is characterized by its "pursuit of minute-level visibility." While other models also offer high visibility, the T1 is the only Sinn model to feature an arrow-shaped minute hand that makes the minute hand even more noticeable.

　In addition, the luminous colors are blue for the indexes on the dial, and green for the minute hand and triangular indexes on the bezel. These innovations, combined with the push-in rotating bezel, improve the visibility of the elapsed time (minute display) from the time the rotating bezel is set to. From this, it can be said that the T1 is designed with a "design concept that prevents errors in measuring minutes."