Are dive computers making bad divers?

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bfw

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Kind of a funny way to bring a 6-year-old thread back from the dead, because dive computers are both more accurate than dive tables, and they are more precise than diver tables. Accuracy and precision - Wikipedia

They measure your depth in typical increments of 0.1ft/0.1m versus of 10ft/3m for tables, and typical increments of time of 1-5 seconds instead of 60 seconds for tables. Dive watches make measurements of similar precision, of course, but the tables themselves are about an order of magnitude less precise than computers.

And for multi-level dive profiles (that is, anything besides a perfect square), they will also measure your depth over time more accurately. Even for square profiles, the accuracy captured by the dive computer is a little better as well, due to their improved precision.
Everything you describe is a difference in precision, not accuracy.

measurement in smaller increments is a difference in precision, not accuracy.

Both the tables and computers represent algorithms that fall in the category of numerical methods, where the differences all deal with data resolution, i.e. precision.
 

EFX

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Everything you describe is a difference in precision, not accuracy.

measurement in smaller increments is a difference in precision, not accuracy.

Both the tables and computers represent algorithms that fall in the category of numerical methods, where the differences all deal with data resolution, i.e. precision.
No. This is wrong. The PADI tables, I believe, are based only on one tissue compartment with a half-time of 120 minutes. Dive computers using ZHL-16C incorporate 16 tissue compartments with varying half-times of which any one compartment can be in control of the dive based on the dive profile. The difference between the PADI tables and DC's then, becomes a matter of accuracy. DC's are also more precise.
 

Brett Hatch

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Everything you describe is a difference in precision, not accuracy.

measurement in smaller increments is a difference in precision, not accuracy.

Both the tables and computers represent algorithms that fall in the category of numerical methods, where the differences all deal with data resolution, i.e. precision.

Let's be clear that I'm not trying to make a semantic argument here. What I mean by accuracy is captured well in the Wiki on this topic: Accuracy and precision - Wikipedia

Wikipedia:
Accuracy and precision are two measures of observational error. Accuracy is how close or far off a given set of measurements (observations or readings) are to their true value, while precision is how close or dispersed the measurements are to each other.

I agree with you that computers are more precise than tables, because the measurements are made with finer granularity; this is the definition of precision.

Setting aside precision, tables are accurate for square profiles only. That is, for a dive profile where the diver descends to the bottom, remains near that depth for the duration of the dive, and then ascends to the top (or to their stop) at a well-known ascent rate. Within the parameters of a square dive profile, dive computers are not meaningfully more accurate than tables.

But for any other dive profile, computers are more accurate. This is because the observations made by the computer will be very close to the diver's true profile, which is the definition of observational accuracy.
 

boulderjohn

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No. This is wrong. The PADI tables, I believe, are based only on one tissue compartment with a half-time of 120 minutes. Dive computers using ZHL-16C incorporate 16 tissue compartments with varying half-times of which any one compartment can be in control of the dive based on the dive profile. The difference between the PADI tables and DC's then, becomes a matter of accuracy. DC's are also more precise.
This is not correct.

The full PADI tables are based on a lot of published research using multiple theoretical tissues. I don't recall the number off the top of my head.

What you are confusing this with is surface interval. Surface intervals are based upon what is believed to be the one controlling tissue in play for that purpose. When the US Navy added the 120 minute tissue to the original set, they made that the tissue controlling surface intervals. They really did not do any research in making that decision, and it did not matter to them, because navy divers generally only do one long dive a day.

It mattered to recreational divers, though, because they typically do 2 or more shorter, shallower dives a day. That 120 minute compartment led to extremely long surface intervals, and it was the opinion of the PADI's lead researcher (Spenser) that this was too long for typical recreational dives. Their research indicated that for the overwhelming majority of recreational dives, the 40 minute compartment was sufficient, but they ultimately decided to use the 60 minute compartment.

Summary:
  • PADI tables use multiple tissues in determining NDLs.
  • The US Navy tables used the 120 minute compartment to calculate surface intervals.
  • The PADI tables use the 60 minute compartment to calculate surface intervals.
 

Akimbo

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They really did not do any research in making that decision, and it did not matter to them, because navy divers generally only do one long dive a day.

Just for clarification, the great majority of working dives in the US Navy are for ships husbandry so are rarely deeper than 40'/12m. These divers often make two or more dives per day. Except for lunch breaks, most surface intervals are waiting on other things to happen like cycling pumps or heavy pieces being rigged.

You are correct that the few jobs that are deep enough to require decompression stops are rarely more than one dive/day/diver. The surface crew is usually large enough that the day is over before all the divers get wet. It is also rare the work requires more than one diver to be in the water at a time.

The majority of the world's combat swimmers use pure Oxygen rebreathers so don't worry about decompression at all. There really isn't much motivation for navies to spend money on decompression research anymore. The tables they have a fine and any serious decompression justifies using saturation divers.

I never would have thought that recreational and a few scientific divers using rebreathers would be driving the cutting edge of decompression theory. Unfortunately research funding is hard to come by.
 

BRT

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Let's be clear that I'm not trying to make a semantic argument here. What I mean by accuracy is captured well in the Wiki on this topic: Accuracy and precision - Wikipedia



I agree with you that computers are more precise than tables, because the measurements are made with finer granularity; this is the definition of precision.

Setting aside precision, tables are accurate for square profiles only. That is, for a dive profile where the diver descends to the bottom, remains near that depth for the duration of the dive, and then ascends to the top (or to their stop) at a well-known ascent rate. Within the parameters of a square dive profile, dive computers are not meaningfully more accurate than tables.

But for any other dive profile, computers are more accurate. This is because the observations made by the computer will be very close to the diver's true profile, which is the definition of observational accuracy.
When was your last square dive? I don't remember ever making one.
 

dmaziuk

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This is not correct.

The full PADI tables are based on a lot of published research using multiple theoretical tissues. I don't recall the number off the top of my head.

What you are confusing this with is surface interval. Surface intervals are based upon what is believed to be the one controlling tissue in play for that purpose. When the US Navy added the 120 minute tissue to the original set, they made that the tissue controlling surface intervals. They really did not do any research in making that decision, and it did not matter to them, because navy divers generally only do one long dive a day.

14 compartments and they added the 60-minute one and a few others. Workman's set (US tables) has 40 minutes, then 80.

They added a couple of extra slow ones too, only to find out during testing that they never mater: even the 120-minute one takes 6 days of diving to get anywhere near its M-value. Hence the 6-day schedules that are still around at many popular diving destinations.
 

Akimbo

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Have you ever wondered why Bühlmann chose 16 or 32 compartments (ZHL-16 and ZHL-32) for his algorithms? It has nothing to do with human physiology, it is for optimum computer memory usage. It didn't matter when Dr Workman was using a slide rule.
 

dmaziuk

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Have you ever wondered why Bühlmann chose 16 or 32 compartments (ZHL-16 and ZHL-32) for his algorithms? It has nothing to do with human physiology, it is for optimum computer memory usage. It didn't matter when Dr Workman was using a slide rule.

Well now that you mention it... Baudot codes are 5 bit and IBM made 6-bit computers for a while. Including these: The IBM 4020 Military Computer – Tracking Missiles with 6-bit Bytes | The CPU Shack Museum

Powers of two and hence: 8-bit bytes, are actually fairly recent. Apparently they ended up making hardware design easier and won the market.
 
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