Dive computers... SO many choices!

[scubadada]

@stuartv Ah yeah, no worries. I wasn't taking it directly. lol

Should have been more specific with the sentence about "high values like 95"... i mean both low and high GF values that are numerically high.

Im wondering if the DSAT profiles versus a ZHL-16C GF High of 95 are just comparing square profiles, or multilevel dives? Im thinking about drift between the algorithms when the active tissue compartments start to shift, I don't know much about how DSAT is structured and calculated.

You are correct, that's why I said GF hi of 95 was a good approximation of DSAT. It does vary by depth, better fit at shallower rec depths. I don't know much about DSAT either, it is proprietary. I just have a lot of experience with it. The derivation of DSAT is well documented and tested, the basis for PADI tables.

 

[Rred]

Speaking of varying algorithms and times...I see most dive computers can display the ambient temperature, but I haven't seen them mention if they are accounting for that in their calculations. The "standard" USN dive tables that many of us started with, were officially "warm water tables" and the USN quietly but clearly said "If you need to wear a wet suit or you feel cold, you should use the cold waters tables instead." Which was basically one time/depth group "up", what would be called one additional personal safety/comfort factor now.

So I'm wondering, do any of the computers adjust their tables, based on ambient temperature? In theory, that has to be accounted for in order to calculate safe times. Perhaps that's quietly a part of why some computers are 'too conservative" compared to others?

And after reading a lot of publications from DAN and other sources, and seeing how diving (tables, safety stops, ascent rates, etc) procedures have changed because of research into things like micro-bubble formation...I like to stay on the conservative side. The new research keeps turning up factors that have gone unseen, that seem to influence whether a diver (especially an older diver) will get hit. And paralysis is just something I'd rather do without.

 

[dmaziuk]

Speaking of varying algorithms and times...I see most dive computers can display the ambient temperature, but I haven't seen them mention if they are accounting for that in their calculations. The "standard" USN dive tables that many of us started with, were officially "warm water tables" and the USN quietly but clearly said "If you need to wear a wet suit or you feel cold, you should use the cold waters tables instead." Which was basically one time/depth group "up", what would be called one additional personal safety/comfort factor now.

So I'm wondering, do any of the computers adjust their tables, based on ambient temperature? In theory, that has to be accounted for in order to calculate safe times. Perhaps that's quietly a part of why some computers are 'too conservative" compared to others?

That would work if they were measuring ambient temperature inside the diver's suit. Otherwise: not so much.

 

[Rred]

dm-
No need to get inside the suit and measure body temperature, although that would be desireable. The use of cold water compensation (cold water tables) is for anything that would cause a typiucal diver to wear a wet suit. So, when Florida divers say "Wow! It's 73F I'm glad I have my 3mm wetsuit!" that's arguably time for cold water compensation, based on the water temperature alone. The same way that water would cause hypothermia. Sure, a new England diver in 50F water and a 1/4" farmer john may actually BE warmer...but the same rule applies, if you need a wet suit, you are supposed to be on the cold water tables. (And that's directly from a USN chief diving medical officer, who had a chest full of fruit salad showing he wasn't just a desk jockey.)

Using the ambient temperature is "the best you can do" without sticking a thermocouple in the diver, so it is still a worthwhile goal, and more likely to be correct than simply ignoring the temperature.

 

[scubadada]

Personally, I am skeptical of the temperature monitoring and the heart rate monitoring. I would not invest in this technology. I would ask Scubapro to provide the data to support these practices. When I am cold, my air consumption does go up, this variable might be valid.

 

[dmaziuk]

All I could find in ScubaPro's marketing blurbs is that they monitor breathing rate to adjust Guesstimated Time Remaining, I doubt they do anything with body temp.

@Rred: I don't need no stinking wetsuit in the tropical Caribbean waters. On dive 1. On day 2 I start wearing a rash guard under my shorty and on day 7 I sleep under a down blanket in 30C heat. What warms me up is the thought that my scary conservative dreaded folded RGBM computer gets less liberal with each dive. I.e. as I get colder, is quietly shifts my pressure groups towards "one up", just as you suggest.

 

[stuartv]

Speaking of varying algorithms and times...I see most dive computers can display the ambient temperature, but I haven't seen them mention if they are accounting for that in their calculations..

Ones the implement Buhlmann ZHL-16B or C or VPM-B do not. Those algorithms do not have a parameter for temperature (or SAC or heart rate) in their calculations.

ScubaPro is the only one I can think of that claims to factor in anything more than just depth, time, and gas blend. Some of their computers even come with a heart rate monitor that the computer factors in. And they say the HRM also measures skin temperature, which is also factored in. Example:

http://www.scubapro.com/en-US/USA/instruments/computers/products/m2.aspx

From that page:

"SCUBAPRO's ZHL-8 ADT MB PMG is the only dive computer algorithm that includes a diver's breathing rate, heart rate and skin temperature as an indicator of workload during a dive and adjusts the decompression plan to avoid risk factors."

I would guess that that means they do some Buhlmann-based calculation and then they use those other factors to make it more conservative sometimes, but never more liberal.

It sounds great on paper. But, I'm kind of "over" using proprietary algorithms, personally.... I'm okay with a proprietary implementation of a public domain algorithm, but not knowing what the algorithm does or is supposed to do is not where I want to go any more.

 

[ls1dreams]

]But, I'm kind of "over" using proprietary algorithms, personally.... I'm okay with a proprietary implementation of a public domain algorithm, but not knowing what the algorithm does or is supposed to do is not where I want to go any more.

This is exactly why I'm looking at DC's that have established, known algs. The problem is that when people experiment/tinker with the algorithms, you get things that act like deep stop/RGBM models which are NOT scientifically proven. Even the BHL-8DAT hybrid does some of that.

To me, a rec dive computer should mostly be low touch 95% of the time, but for emergency situations where I might accidentally go into deco, i'm damn well prefer to be using a proper ascent model and force my buddies to come up with me, rather than simply deciding on gradients to match their incorrect model devices.

@stuartv: if you were limited to a single lo/hi setting for a rec computer that would be 98-99% within NDL limits, but 1-2% of the time requiring modest deco, what would you set the gradients at?

Even if we can't set manual gradients for a rec computer (which I agree is a bit overkill), it would be ideal if at least ONE of the settings matches those factors.

 

[stuartv]

@stuartv: if you were limited to a single lo/hi setting for a rec computer that would be 98-99% within NDL limits, but 1-2% of the time requiring modest deco, what would you set the gradients at?

Well, I am very flattered that you would ask me that question. But, I have to say that, while I can talk a great game about a lot of this stuff, I have only been diving a bit over 2 years, I only have 122 dives in my log, and only have about 10 or 12 real deco dives under my belt so far. So, I really do not feel like I can give you a good answer for that question. I have done a lot of reading. But, my real world experience so far has taught me that what I think after just doing a bunch of reading isn't always right.

I would not recommend to anyone to go into deco that has not gotten training for doing deco. So, I would not recommend deco settings for anyone that hasn't had that training. I really don't mean to sound like a d!ck when I say that. I just feel like there is enough to the whole process of doing a dive that involves deco that by the time I could give you my complete opinion on the answer to you question, I would have had to more or less give you a whole deco class - and I am definitely not qualified to do that. So I just have to say there is no short, simple answer to your question. Or, if there is, I have not yet learned enough to tell it to you.

If you really want to get an answer to your question without anteing up to actually take Deco Procedures, I would recommend 2 books for you to read:

Deco For Divers, by Mark Powell (Deco for Divers: A Diver's Guide to Decompression Theory and Physiology: Mark Powell: 9781905492299: Amazon.com: Books),

and,

The Six Skills, by Steve Lewis (The Six Skills and Other Discussions: Creative Solutions for Technical Divers: Mr Steve Lewis: 9780981228020: Amazon.com: Books).

They are both great reads. Neither one is especially thick. They are both written for regular shmoe divers to be able to understand - though Powell does get technical enough at times that you CAN get lost for a page or two. But, he always brings it back to a reasonable level. It's clear he kept it in mind at all times that his audience is divers, not deco scientists.

Steve's book is about a lot more than just deco theory. It's actually not really about deco THEORY at all. But everything he talks about has some relevance to the ultimate question of how you plan your dive - of which, choosing a deco algorithm and its parameters is one important part.

If you read those two books, I think you will have a much better idea of the best way to answer your question.

 

[BoltSnap]

I just went back to the OP to check what was the original question, talk about SEVERE topic drift

Somebody is asking about what "pencils" to use in their first grade and the discussion went into post Ph.D. discussions.