Weeks ago I had the pleasure to handle in metal, thanks to my Italian buddy Luigi a brother for me.. a beautiful vintage diver from the 70s.
A purpose built instrument a tool watch belonging to a different era where real divers relied on nothing but a depth gauge and a mechanical dive watch to explore the bottom of the sea.
“When first launched in 1961, the Vulcain Cricket Nautical was truly avant-garde in all respects. For the first time ever, a wristwatch was capable of descending to 300 meters and audibly warning its wearer that it was time to the surface, while precisely indicating the various decompression stops."
The compressed air a diver breathes contains the same amount of inert nitrogen as the air we breathe at the surface. But the deeper you dive and the longer you stay down, the more of this nitrogen is absorbed by the body. When a diver ascends, this nitrogen expands and, if all goes well, is harmlessly released through the bloodstream. But stay too deep for too long, or ascend too quickly, and the nitrogen can rupture tissue, damage blood vessels and nerves, and wreak havoc on the body.
With no dive computers, at the time recreational divers were forced to abide the dive tables developed by the US Navy that dictate the decompression limit for each depth.
As long as you don't exceed the deco limits time, you can safely resurface without getting the bends.
Most often, divers exceed these no-decompression limits deliberately, in order to explore a deep wreck for example, so to safely surface from these dives, they must linger at set depths on the way up and “decompress.”
Decompression diving uses its own set of tables which outline at what depths and for how long a diver must decompress on his way up. These tables would be cumbersome and inconvenient for a diver to carry while submerged, so Vulcain, with the help of Dr. Keller, put these tables on the dial of the Nautical Cricket.
Without further ado, it's time to see how to read the dive table on the Vintage Nautical Cricket Diver from the 70s which I tried on my wrist, feeling so darn stupid by the way since I'm not a diver and I never bothered to learn something about dive tables till that day.
The first thing to keep in mind is, it's just an analog watch made to tell the time, so forget for a moment all those colored circles, forget those strange numbers printed on them, forget the alarm and the seconds hands.
So what do we have here? hour and minute hands, minute markers and minutes scale printed inside the black circle of the inner rotating bezel.
So far nothing difficult, heck, we learned how to read the right time when we were just puppies.
Let's move forward to the white squares track now.
We can see two columns of numbers printed in black, 40-135, 35-115, 30-100, 25-85.
At the top of each column we can see also two letters, M\F printed in white.
What do they stand for? M stands for meters, F stands for feet. Those columns of numbers represent the depth scale, so 40mt = 135ft - 35mt = 115ft and so on...
Now, let's say we are planning a dive to enjoy the beautiful coral reef at 25mt depth = 85ft below the surface, with our Vulcain diver strapped over the wetsuit.
All we need to know is how many minutes we can stay at that depth without the need to make a deco-stop.
Just follow the 25/85 white squares curve track till the number 0.. the square is orange now, why?
0 is our No-Decompression-Limit, so we can enjoy the dive at 85 ft depth without the need to make a deco stop for.... follow the minute markers scale now and see where the 0 square is located.. the NDL is 34minutes.
But what does happen if we stay at that depth for 35 minutes, just a minute more?
We are forced to round up our math since we can't ascend quickly and safely anymore due to the higher quantity of nitrogen accumulated in our body that would be lethal for us, so let's follow the curve again till the next orange square with the number 5.
Number 5 is the time of minutes we need to stop usually at 15ft depth before resurface safely.
Actually, what the table is telling us is this, 5min is the first deco stop necessary if your dive time is 40minutes at 85ft depth.
But if we can stay down 50 minutes for example, according to the table our the decompression stop will increase to 20 minutes. (Number actually covered by the hour hand but it's there.)
Alright, time for a quick recap.
85ft depth = NDL 34minutes
40 minutes at 85ft depth = 5min. stop at 15ft
50 minutes at 85ft depth = 20min. stop at 15 ft
Different depth zone, same logic and same way to read the table.
100ft depth = NDL 19 minutes
25 minutes at 100ft depth = 5min. stop at 15ft
35 minutes at 100ft depth = 15min. stop at 15ft
45 minutes at 100ft depth = 30min. stop at 15ft
55 minutes at 100ft depth = 45min. stop at 15ft
115ft depth = NDL 13 minutes
20 minutes at 115ft depth = 5min. stop at 15ft
30 minutes at 115ft depth = 25min stop at 15ft
40 minutes at 115ft depth = 40 minutes stop at 15ft
50 minutes at 115ft depth = 60 minutes stop at 15ft
135ft depth = NDL 10 minutes
10 minutes at 135ft depth = 10min. stop at 15ft
25 minutes at 135ft depth = 30mins stop at 15ft
35 minutes at 135ft depth = 45 min. stop at 15 ft
45 minutes at 135 ft depth = 60min. stop at 15 feet
55 minutes at 135ft depth = 80 min. stop at 15 feet
Hope I made no mistakes , but that is all gentlemen, finally we have been able to understand and to read a very cool yet useful feature at the time.
Sorry for the headache, and many thanks for looking!