The patent that defined the modern Swiss dive watch.
Filed 15 May 1964 by Marc Jasinski for Aquastar S.A. of Geneva (CH 436 140), the Deepstar bezel is the world's first multiple-dive no-decompression chronograph mechanism. It made the watch a dive-planning tool in the tool-watch tradition. It carries two scales, an inner 60-minute elapsed-time scale and an outer no-decompression scale calibrated to the French Navy tables of the period, and lets a diver plan a first dive, time the surface interval, and execute a repetitive second dive directly off the wrist, without a slide rule and without a separate table.
Sixty-two years later the geometry is unchanged. Every modern Aquastar Deepstar carries the bezel pattern that came off the original 1962 blueprints.
How it works: a worked example.
To understand the bezel, it helps to walk through a worked example using the same 1960s French Navy decompression table the bezel was calibrated against. The scenario below is the standard repetitive-dive plan a Marine Nationale combat diver would have read at the time.
First dive.
Pick a hypothetical depth for a first dive and find the corresponding maximum bottom time on the table. A dive to 39 meters (approximately 130 ft) for 25 minutes. Where depth and time intersect, the table gives two numbers. The primary number is the mandatory decompression time for the dive in minutes. The second number is the partial pressure of absorbed nitrogen in the body, known as "Coefficient C." This Coefficient will be used later during the surface interval, before the repetitive dive.
Now look at the Aquastar bezel itself. It has two scales, an inner scale and an outer scale. The inner scale is the traditional 60-minute elapsed-time scale found on every other dive watch. The outer scale is the key to calculating repetitive dives.
Before jumping in, the diver aligns the zero marker, the lumed pip on the bezel, to the minute hand, the standard procedure for measuring elapsed dive time. During the dive, the minute hand advances on the inner scale, showing how many minutes have passed at 39 meters. When the hand reaches the 25-minute mark, previously planned, the bottom phase is over and it's time to ascend to the decompression stop. The decompression stop should be made for 15 minutes, after which the ascent to the surface should be completed.
Surface interval.
Once at the surface, the outer scale is used to factor nitrogen off-gassing in preparation for the second dive. Here's where the previously determined Coefficient C, say 1.6, is used. The 1.6 value on the outer scale of the bezel is now aligned with the hour hand. As the hour hand advances, the bezel shows the decreasing values of absorbed nitrogen, 1.5, 1.4, 1.3, 1.2. If the value has not decreased below 1.4, the concentration of nitrogen in the body is still too high, and a second dive cannot be made.
Second dive.
The second dive is planned for a shallower depth, say 30 meters. The second dive should always be shallower than the first.
Scenario A. If we look at the outer "P=55-12 meters" scale and find the 30 (the planned dive depth), the 6-minute mark on the inner scale aligns with the 30 m mark on the outer bezel. This 6 minutes is the time "handicap", the penalty time to subtract from the second dive. When enough surface time has passed and the hour hand passes from the original Coefficient C of 1.6 down to a new Coefficient C of 1.1, that full 6-minute penalty applies. Going back to the table, the 30-meter depth with a planned 30-minute dive becomes 24 minutes of actual bottom time. The decompression time stays as the table specifies, a 3-minute mandatory decompression, and according to the table the new Coefficient C after this second dive is 1.5.
Scenario B. If the surface interval was shorter and the hour hand has reached only the 1.3 range, the number on the right of that range, "3" in this example, is used as a multiplication factor on the 6-minute penalty: 6 × 3 = 18 minutes are subtracted from the 30-minute planned dive. The second dive shrinks to 12 minutes. At the 1.2 range, the multiplier is 2: 12 minutes are subtracted, leaving an actual dive of 18 minutes.
If the surface interval passes beyond the 1.1 range and into the "Normal" section of the scale, all nitrogen is considered to have off-gassed from the body. At that point a "second" dive can be planned as a fresh first dive, with no handicap.
Historical context.
The Deepstar bezel was developed and patented on the basis of the scientific research conducted in the early 1960s on gas saturation in the human body during diving. The worked example above is provided for historical verification of the bezel's design intent and is not a current diving recommendation. The 1960s French Navy decompression tables have been replaced or updated since; modern diving practice relies on personal dive computers and the current decompression algorithms maintained by the standards bodies. The bezel on the watch remains, and reads, exactly as it was designed in 1964.
How to read the bezel: a worked example.
The previous walk-through covers the math behind the scale. The five steps below restate the same procedure in the order a diver actually performs it on the wrist, from the moment the bezel is set on the surface to the moment the repetitive dive begins.
- Align the bezel zero against the minute hand before descent. On the surface, rotate the outer bezel so the lumed zero pip sits against the minute hand. This is the standard procedure that any 60-minute dive bezel uses to time elapsed minutes. On the Deepstar it also primes the outer no-decompression scale to be read off the same hand during the dive.
- Read elapsed time on the inner 60-minute scale during the bottom phase. During descent and at depth, the minute hand advances around the inner 60-minute scale. The reading is elapsed dive time. The diver compares it against the maximum bottom time read from the French Navy table for the planned depth and ascends when the planned bottom time is reached.
- Ascend, execute the decompression stop, and surface. The mandatory decompression time at the stop is read directly from the French Navy table at the intersection of depth and bottom time. The bezel does not change role during this phase; the minute hand on the inner scale still shows elapsed time. On reaching the surface, the diver notes the Coefficient C the table returned for the first dive.
- Re-align the bezel against the hour hand for the surface interval. On the surface, the diver rotates the bezel so the Coefficient C value from the first dive on the outer scale sits against the hour hand. As the hour hand advances, the outer scale shows the dropping nitrogen coefficient as the body off-gasses. The bezel makes the falling coefficient visible at a glance, without a slate or a slide rule.
- Read the penalty and execute the repetitive second dive. Locate the planned depth of the second dive on the outer no-decompression scale. The reading aligned on the inner scale is the time penalty to subtract, multiplied by the factor shown on the current coefficient range. Subtract the penalty from the planned bottom time of the second dive, then dive. If the hour hand has passed into the Normal section of the scale, no penalty applies and the second dive can be planned as a fresh first dive.
What this bezel solved.
Before 1962, a working diver did not carry the decompression tables on the wrist. The standard tools were a slate to write planned and actual depths, a printed table memorised or carried in a pocket, and in many cases a circular slide rule strapped to the wrist or clipped to the buoyancy gear. Repetitive dives demanded that the diver consult the table on the surface, recompute the bottom time penalty by hand, and trust the math before going back down. The arithmetic was simple, but the moment a diver had to do it was a moment they were not focused on the next dive.
The Aquastar solution put the decompression math on the bezel itself. The inner 60-minute scale handled elapsed time the way every dive bezel since has handled it, and it sits apart from the elapsed-time and count-up designs covered in our guide to how every type of dive bezel works. The outer scale, calibrated to the French Navy tables of the period, let the diver align the Coefficient C against the hour hand, read the falling nitrogen value as the surface interval ran, and resolve the repetitive-dive penalty by reading a single mark off the inner scale. The slide rule moved from the wrist strap onto the bezel.
That mechanical layer mattered once electronic dive computers arrived. A computer can fail at depth from a battery, a flooded case, or a software fault, and when it does the diver is left with whatever they can read off the wrist. The Deepstar bezel was designed as the primary instrument, and on modern Deepstar references it still gives a working diver a calibrated fallback to plan an ascent and a surface interval without an electronic device.
Frequently asked questions.
What is the no-decompression bezel?
It is a rotating dive-watch bezel carrying two scales. The inner scale is a 60-minute elapsed-time scale; the outer scale is calibrated to a set of decompression tables. Together they let a diver plan a first dive, time the surface interval, and execute a repetitive second dive directly off the wrist, without a slate or a slide rule.
Who invented the no-decompression bezel?
The bezel was designed by Marc Jasinski for Aquastar S.A. of Geneva. It was the first dive-watch bezel built to resolve repetitive-dive math against a national-navy decompression table.
When was the no-decompression bezel patented?
The Swiss patent CH 436 140 was filed on 15 May 1964. The bezel geometry on every modern Aquastar Deepstar reference is the same geometry described in that patent.
Why is it still used today?
Modern dive planning runs on electronic dive computers, but a computer can fail at depth. The bezel is a mechanical instrument that does not need a battery or firmware to read, which is why working divers still value it as a redundant planning tool on the wrist.
Which Aquastar models still carry the bezel?
Every modern Aquastar Deepstar reference carries the patented bezel pattern off the original 1962 blueprints. The Deepstar collection page lists the current references.
Where to go next.
See the Deepstar collection: every modern Deepstar carries this bezel.
Read about the column-wheel calibre: the chronograph mechanism that sits below the bezel.
Read the eleven patents: the full archive including CH 436 140 (Jasinski, 1964).
The best Swiss tool watches: where the dive chronograph sits among purpose-built watches.
