SHARP & Mido
Every great diver’s watch has two main things going for it: tough construction and unique looks. The former assures the watch will perform as intended underwater – including water-resistance, high visibility in low light and a timing bezel – while the latter gives you something to admire every time you check your wrist on land. Mido’s new Ocean Star Decompression Timer 1961 ($1,450) does both of these things with aplomb, which goes a long way to explaining the popularity of this ‘60s-inspired limited-edition. Unlike most dive watches, however, which feature a unidirectional rotating bezel that allows divers to monitor their air supply, this unusual piece also offers something else: a decompression timer that’s as colourful as it is functional. Here’s how it works.
What is decompression?
Decompression happens when a diver ascends back to the surface at the end of a dive, and must re-adjust from the higher pressure at depth to a lower pressure at the surface. Ascend too fast and nitrogen bubbles can form in the blood, leading to decompression sickness (aka the bends). For this reason, it’s very important that divers ascend methodically and slowly using “decompression stops” to ensure a safe return to the surface, and that’s precisely what this watch was designed to help with.
Check your depth
In addition to an hour track on the centre and a minute track around the edge, most of the Ocean Star Decompression Timer 1961’s dial is dedicated to a bright, colourful decompression time indicator. This takes the form of four concentric coloured rings (yellow, green, pink, and blue) each of which correspond to a dive depth. First, you’ll need to select your dive depth using the scale at 12 o’clock. The depths are indicated in metres on the left (25/30/35/40) and in equivalent feet on the right (80/95/110/130). So if you’re diving to a depth of 25 metres / 80 feet, you’ll use the yellow ring, if you’re diving to 30 metres / 95 feet, you’ll use the green ring, etcetera, up to a maximum of 40 metres or 135 feet.
Once you’ve got your dive depth, the next step is to read the decompression times indicated in a circle around your particular depth ring. Because your decompression time is relative to your total dive time (the longer the dive, the more decompression required) the indicator will tell you how long your decompression stop should be based on how long you’ve been underwater. For example, for a 25m-29m dive (yellow ring), stops are indicated after 34 minutes. So from 35-40 minutes, you’ll need a five-minute stop, from 41-50 minutes a 20-minute stop is required, and so on.
To make use of the timer, begin by setting the minute hand to 12, and then use that hand to time your dive. When you reach your decompression stop, you can time its duration using the rotating bezel. Just turn the bezel until the numeral corresponding to your decompression is aligned with the minute hand (numeral 20 for a 20-minute stop, say). Then, when the minute hand reaches zero (marked by the luminescent pip on the bezel), you can safely return to the surface.
While most people will never use their Mido to time a dive (and indeed, Mido doesn’t suggest relying on the watch in place of a modern dive computer) a big part of the pleasure of owning this colourful and historic piece is understanding how the feature works.