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When the 300 was first released, this question popped up a couple of times, but was never answered in everyday terms. Sure, the Jenny website makes available a copy of the original 1971 patent, but unless you're a patent lawyer, well versed in wading through the legalese, it can be difficult to comprehend. Since I had a chance to dive with one back in March, I thought I'd explain the numbers...so that even the most novice desk diver, can easily understand.:)

Alright, let's take a close look at the bezel, and focus on the first two segments of the three concentric rings that allow us to calculate for decompression, and non-decompression dives. The first ring segment, closest to the dial, contains the number 60...with the number 5 resting on the dividing line. The 60 is your depth reading, and the 5 is the traditional elapsed time numeral of a conventional diving bezel. Now let's look at the center ring segment that contains the numerals 60, 70, 80, and 100. These are your bottom time numbers, and we'll come back to these in a moment. Now let's look at the third, and outermost ring segment, which contains the numerals 0, 2, 7, and 14. These are your decompression, and non-decompression times.



Now it's time to make a dive. We jump in, and we make a dive down to 60 feet. We know that because our depth gauge tell us, so now we look at our watch to find the 60 on the innermost ring. Above that, in the center ring we see 60, 70, 80, and 100...like I said before those are dive times. If we stay 60 minutes at 60 feet, how much decompression do we have? Let's look at the outer ring...the number above 60 is 0, so we have 0 minutes of decompression...a classic, recreational, non-decompression dive. What if we stay 70 minutes, at 60 feet? The 2 is above the 70, so we have 2 minutes of decompression. Same goes for 80, you'll have 7 miutes of decompression, and if you stay for 100 minutes, you'll have 14 minutes of decompression.

In the next segment, you see a 70 on the innermost ring...that's for a 70 foot dive. If you stay 50 minutes at 70 feet, you have 0 minutes of decompression. If you stay 60 minutes at 70 feet, you'll have 8 minutes of decompression, a 70 minute dive would require 14 minutes of decompression, and an 80 minute dive would require 18 minutes of decompression. The other segments are used in the exact same way, allowing for a maximum planned depth of 170 feet.

Below is a copy of an original instruction booklet for the Caribbean 1000, in German. You'll notice that unlike modern decompression diving, where decompression stops are staged throughout a range of depths...all of these deco stops are to be made at 10 feet. I'm guessing this goes back to a simplified version of the Haldane tables, for which John Scott Haldane was the forefather of modern decompression diving.




So did I make any decompression dives, planned according to this bezel? No, but it's cool to know that if I happened to overstay my non-decompression dive time...I'd have a chart that would help me calculate my mandatory decompression, so I could make it back home safely. :-!
 
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