Suggestions for getting my first dive computer

[Diving Dubai]

This - taken from the Lite Deco thread - Slightly edited to to remove the parts that would be out of context (i.e. referrals to previous comments)

Certainly sums up my feelings on the matter, however everyone is entitled to their own opinions.

An NDL is determined by the mathematics of a given, specific, decompression algorithm. It's not a grey area. It's not fuzzy. It's a very clear number on a table or computer screen.

Different algorithms provide different NDL for otherwise identical dive parameters. In addition, most algorithms can be made more conservative via manual settings - reducing the NDL.

However, DCS presentation itself IS a grey area. There are a myriad of known factors that can vary the potential onset and severity ...and probably quite a few unknown factors also.

It's important to recognise that diving within a given algorithm NDL is not a guaranteed assurance that you won't get DCS.

Pertinent to some stances in this debate, it's also correct to recognize that exceeding an NDL is also not a guaranteed assurance that you will get DCS.

Divers increasingly have the freedom to select an NDL for their diving. Gone are the days when the only choice for most divers was between a PADI table NDL and a US Navy table derived NDL.

There are now dozens of dive computers on the market, running many different algorithms... each calculating more conservative premises aggressive diving limits.

Very few recreational divers select a computer based on algorithm concerns. The algorithm is barely mentioned in most dive computer advertising. When it is mentioned, most divers aren't knowledgeable enough to place it into a personal context or risk consideration.


I'd agree that any dive has physiological effects on the body; including effects that persist post-dive. This includes the formation of bubbles.

However, those physiological effects may not be significant enough to create diagnostic signs or symptoms according to the current criteria of DCS. That does not mean that these effects are non-damaging in ways, as yet, not understood by hyperbaric medicine.


There's undoubtedly physiological factors that make some individuals highly prone to DCS. Vice-versa, there's individuals that can do extraordinarily aggressive diving and seem near-immune to DCS.

This is why the general advice is always to dive conservatively. Historically, that's been through staying comfortably within an NDL. In the age of diving computers and varied algorithms, it also means choosing a conservative algorithm and/or setting for an algorithm.

Obviously, it takes significant diving experience to determine your own personal risk factors with DCS. Each dive adds to your individual sample... your personal statistics.

I'd suggest that it takes many hundreds, if not thousands, of dives to confidently determine your general susceptibility to DCS.

Even then, your susceptibility will vary depending on many factors, not least your age, general health and fitness. A prudent diver should expect increasing susceptibility as they get older and/or if their diving habits change.

Paying attention to your post-dive vitality may help a quicker understanding of your susceptibility, without the need to push your 'sampling' to the level where you need hyperbaric medical treatment.

Obviously, to achieve this requires both experience and astute observation.

But that still sucks for the few it doesn't work for.

It pays to stay very conservative until you have a high degree of confidence in understanding your own DCS susceptibility.

Many divers erring towards aggressive diving seem to underestimate the time and parameters needed to have that real confidence.

 

[Storker]

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A ScubaBoard Staff Message...

OK, everybody. Take a deep breath or three and calm down. This is the New Divers forum, which has its own special rules:

Please note: This forum has special rules. This forum is intended to be a very friendly, "flame free zone" where divers of any skill level may ask questions about basic scuba topics without fear of being accosted. Please show respect and courtesy at all times. Remember that the inquirer is looking for answers that they can understand. This is a learning zone and consequently, any off-topic or overly harsh responses will be removed.

So please remember to answer in a way that's understandable for a new diver, and take any hijacks, like algorithm A vs algorithm B, to the Advanced forum, mmkay?

Further derailments or overtly aggressive and/or snarky replies will be removed without further notice.

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And welcome to the board, @RCPort . As you can see, people here are quite enthusiastic about their sport and some of us may sometimes forget that other members aren't quite as thick-skinned and/or have read as much theory as they have themself. Don't let that scare you from hanging out here

 

[boulderjohn]

Just as an explanation, my previous post related to the ones before that which seemed to imply that all vacation-type diving was done in shallow water with AL 80 tanks (yes, I just exaggerated), which is not true. Some such posts implied that NDLs are never an issue on such dives, which is not true. Some posts implied that the choice of algorithms does not matter to such divers, which is not always true (but often is).

I have been on the sales floor of dive shops a number of times while a customer was considering a computer, and each time the employee went over the pros and cons of the different models available. In the most recent shop with which I worked, the shop became a potential seller of Suuntos when the company was sold. They refuse to stock them because they don't like the algorithm. The shop for which I worked earlier sold almost nothing but Suuntos, so if you went there you would not have had much of a choice.

 

[Rred]

Over the last 45 years, the "standard" safe ascent rate has been cut in half, from 60fpm to not more than 30fpm. And, a "mandatory" safety stop has been added to all dive profiles. Despite these changes, both the USN and DAN continue to research microbubbles in the blood and do research that further refines what is causing a decompression problem. There are no "safe" tables or algorithms, only ones that are more or less conservative, and if you really want to know what you are dealing with, you need to ask "Are these numbers based on what percent of incidents being acceptable?"

I doubt you'll get a number from anyone besides the USN or a similar government body. Sport divers and sport "divemasters" all seem to have their own criteria, such as keeping down the surface interval on double dives, so they can book the boats more frequently. A popular dive in the Florida Keys is The Vanderbilt, and all the dive operators pretty much dive the same profile. Except, that profile violates the USN dive tables even before any additional safety margin is added. Do I care if they have made thousands of dives without getting bent? No. I care about planning my own dive profile, to keep myself out of the chamber and the wheelchair. If the USN tells me that I can and should dive more conservatively than "the divemaster" wants, TFB for the divemaster. The research continues. The profiles keep getting more refined and more conservative, especially for older divers.

 

[dmaziuk]

OK, everybody. Take a deep breath or three and calm down. This is the New Divers forum, which has its own special rules
...
Further derailments or overtly aggressive and/or snarky replies will be removed without further notice.

Can't help wondering, though, about not modding posts giving New Divers provably incorrect statements while modding the ones that call their incorrectness.

 

[packrat12]

The reason for the current ‘safety stop’ came out of research into microbubbles in the late ‘80s and early ‘90s. There was a dramatic reduction by almost 1/2 in microbubbles by adding a little stop at 15’. At that time, microbubbles were thought to be a precursor to DCS so this brought about the ‘safety stop’. Later studies have indicated that they are not a precursor to DCS and are just there. The ‘safety stop’ remained, in my opinion, as a method of building in a little margin to any dive and also to slow down the ascent before becoming a Polaris missile. No longer is it the original reason but unfortunately, I think the training on it does not reflect this. Many divers, and I am not one of them, will put a ‘safety stop’ into an emergency action regardless of reason – crazy IMO. Long before ‘safety stops’ were taught, I recommended one during an emergency ascent to a group of divers – they were well past NDL limits (table even) at that time and were buddy breathing their way up from Blue Springs, Orange City….. (I assume they got bent later as they did not do it)

I would say the pre-computer diving had a tremendous safety margin built into it. We used things like the next deepest depth so a dive at 102’ became a dive at 110’. A dive for 16 minutes became a 20 minute dive. Since we only had a max depth indicator, we could spend a majority of a dive at 80’ but have a max depth of 102’ (110’). While on the surface interval, our time was normally based on when we started to get ready to get in. So a 20 minute SI might be closer to 25 minutes. So again, a really good safety margin was normally built up on the dive profiles. Sure you could dive a square profile but that was rarer.

Now with a computer, we track based on actual depth, time and expected tissue loading. If I follow a computer to NDL, it really is an algorithm based NDL, unlike a table where I might not really be anywhere near it due to rounding and actual vs planned profile. So coming up at or near NDL on a computer really is being near the theoretical NDL of that computer. This is far less conservative than most of our tables were. One of the reasons I first switched to a computer was that I had 3 back-to-back 70’ dives. Never remotely approached NDL limits on the computer. I did the calculation on tables and found I would have been in deco mid second dive. Next day, I purchased a computer for my wife!

I am not about to say that tables are ‘safer’. Too many errors often happened back then. We often bumped our max depth indicator, forgot to time BT, forgot to time SI, etc. I would be interested in actual DCS rates from the ‘80s compared to today, when following the available method of the day accurately. I would be willing to bet that the average table diver doing non square profiles accurately would be more conservative and have had fewer incidents of DCS.

As for the OP: Buy any modern computer you like. If you start diving often, you may find a computer that you prefer and even regret your first purchase, but how would you know now. I used my 1997 puck computers until I started Nitrox almost 15 years later as an example. Another example is my daughter’s boyfriend. We had him purchase a very nice Oceanic ProPlus 3. Great computer except he is starting to go towards the technical environment. Who would have planned that one? He will still get a couple of good years out of it regardless. Once you have experience on your type of diving, then you will be in a better place to purchase the computer type you really want. Personally, buy based on the features you want now but manage the cost of it. I do not believe the algorithm is important until you know you want a particular style of diving and that comes from experience. My only complaint about some algorithms used are those that penalize you unduly. There are some computers that will, to my understanding, add a penalty if you surface too fast, miss a safety or deep stop, etc. I want one that will let me decide how to penalize myself.

 

[stuartv]

If you start diving often, you may find a computer that you prefer and even regret your first purchase, but how would you know now.

I have seen a lot of computers for sale in the Classifieds that were being sold because the owner decided they want a computer that is more liberal.

I have never seen a computer for sale in the Classifieds that was being sold because it was too liberal. I only personally know of one person who replaced their computer because it was too liberal. That person KNEW (not just thought) that it was too liberal because that person got bent, using it. And the only reason the computer needed to be replaced was because that particular (older) computer had a liberal algorithm and did NOT have a Conservatism Factor setting to make it behave more conservatively. The newer computers that I have looked at all have a Conservatism Factor setting.

So, just based on my personal anecdotal evidence, I believe that if you buy a modern computer with a liberal algorithm, and it meets your other needs and desires (e.g. display is a size you like, UI and number of buttons is good for you, etc..) then it's a lot less likely you'll want to replace it (unless it's a recreational-oriented computer and you decide to pursue tech diving). It seems to me that it is a lot more likely (but certainly not a sure thing) that if you buy a conservative computer you'll want to replace it - just because of the algorithm limiting your dive times compared to the people around you.

 

[packrat12]

Stuartv - Actually I know a number of people that prefer a conservative computer algorithm. Not everyone wants to push the NDL and maximize their time. If you start off with a computer you like rather then the algorithm you think you need, the odds are you will enjoy any computer more. I personally have had numerous dives where I surface with both gas and NDL time. Staying down a long time is not my, and many other divers objective. Even a dive like U-352 I was happy to surface even with time and gas avail. Other dives I do, 2 hrs in the Spiegel Grove is not enough for me. In your 2 years or so of diving, you are on at least your 4th (5th? - OCI, Petrel, Sea Bear, Perdix from what I can remember) computer. I do not see that it has been an advantage in your decision making process. I am now on my 5th computer and still have and use all but my 1997 puck (Oceanic Puck, Oceanic PP3, Petrel, Petrel CC, NERD). I have lent my puck to others though, as needed. Each of my computers has a place and need. It is often better to buy what you need then and plan for the future when you gain the necessary experience to understand what suits you best.

 

[stuartv]

Stuartv - Actually I know a number of people that prefer a conservative computer algorithm. Not everyone wants to push the NDL and maximize their time. If you start off with a computer you like rather then the algorithm you think you need, the odds are you will enjoy any computer more. I personally have had numerous dives where I surface with both gas and NDL time. Staying down a long time is not my, and many other divers objective. Even a dive like U-352 I was happy to surface even with time and gas avail. Other dives I do, 2 hrs in the Spiegel Grove is not enough for me. In your 2 years or so of diving, you are on at least your 4th (5th? - OCI, Petrel, Sea Bear, Perdix from what I can remember) computer. I do not see that it has been an advantage in your decision making process. I am now on my 5th computer and still have and use all but my 1997 puck (Oceanic Puck, Oceanic PP3, Petrel, Petrel CC, NERD). I have lent my puck to others though, as needed. Each of my computers has a place and need. It is often better to buy what you need then and plan for the future when you gain the necessary experience to understand what suits you best.

But, do you know anyone that replaced a liberal computer with a conservative one? And do you know anyone that that has replaced a conservative computer with a liberal one? I mean, actually spent money.

If you buy a liberal computer and decide you want to dive more conservatively, you can (with almost all of them, anyway) change the Conservatism Factor to make it more conservative. So, as I said before, if it meets your other needs and desires, you would have no reason to replace it. But, if you buy a conservative computer there is nothing you can do to make it more liberal, in the possible case that you want to have longer bottom times without driving your computer into deco (and thus violating your training).

Notice that I have not said anyone SHOULD buy a liberal computer. I have said they SHOULD understand what the options and ramifications are regarding all aspects of their computer INCLUDING the algorithm. Then decide for themselves what they think will be best for them.


I have had an Oceanic Atom 3.0, Shearwater Petrel 2, SeaBear H3, Hollis TX-1, and Shearwater Perdix AI. I still have all but the Petrel 2.

I did not take the advice of many on ScubaBoard when I was shopping for my first computer and I bought the Atom 3.0 because I wanted a liberal algorithm and AI. The ScubaBoard "experts" all advised against buying a computer based on either of those things.

As it turns out, I am still completely happy with the Atom and if I had not proceeded on to tech diving, I would still be using it as my main (possibly only) computer. Stuart: 1, Scubanati: 0

When I went into tech diving, I really wanted to get the SeaBear H3. But, I decided to listen to the wise and knowledgeable experts here on ScubaBoard and instead I bought the Petrel 2. It didn't take long to regret that decision and when I had a chance to buy an H3 for a discount, I did.

I dived with the H3 and Petrel 2 together for a couple of months and determined that I really did prefer the H3 and really did not like the Petrel 2 very much, so I sold the Petrel 2. Stuart: 2, Scubanati: 0

After I got certified for Helitrox (essentially, beginner's trimix), I could no longer use my Atom as a backup for tech dives. It supports gas switches, but not trimix. I wanted a backup that could handle trimix and also had AI to continue collecting my gas consumption data, as my Atom had been doing for me. I got the TX-1 for cheap. The Scubanati had trashed the TX-1 since I first posted about it over 2 years ago. But, it has served its purpose perfectly well. No regrets there. Stuart: 3, Scubanati: 0

When I bought the TX-1, I had no way of knowing that Shearwater would be releasing a computer with Air Integration. The Perdix AI is way more readable than any LCD (e.g. the TX-1) and works with the same AI transmitter as the Atom and TX-1. Once it came out, it was the obvious choice to replace my H3 as my primary tech computer, with the H3 becoming my backup. Having a highly readable screen (in very low viz) and my tank pressure all in one place is definitely nicer than the situation I was already in with the highly readable screen of my H3, but having to look in a different place (the TX-1 or an SPG) for my tank pressure - neither of which is that easy to read in really low viz. I spotted a killer deal on the Perdix AI, here in the SB Classifieds, and I jumped on it. So, now for all dives, including ones with trimix, I will have a primary computer/SPG all in one that is completely capable and easily readable in very low viz. And I will have a backup SPG and backup computer that is equally capable for trimix and equally readable. For tech diving, I feel like this is pretty much ideal. It would only be better if the H3 would read off the same transmitter. And if the Perdix weren't quite so thick.

I have absolutely no regrets about any of my computer purchases - except for maybe the one that I did purchase based on SB recommendations, instead of going with what I thought I would prefer.

So... what exactly was the point you were trying to make? 'Cause all I've got is "don't listen to the SB experts who tell you to ignore algorithm and who tell you that a Shearwater is the best and if you buy one you'll never regret it." I say, educate yourself about ALL the aspects of dive computers and buy what YOU think you'll like the best. Thus why I don't discount what other people say about considering how easy it is to read, how easy it is to operate, etc.. But I do discount when people say "look at all these things, but ignore this one aspect because you aren't smart enough to understand how to make a choice about that one aspect." I feel like before I even started my original OW class I had a pretty good grasp of the practical differences of the different algorithms and what those differences meant in terms of the computers that I was looking at and how I would use them. It really just isn't that hard. You don't have to know anything about the actual deco theory behind the algorithms to understand what you need in order to make an informed choice of computer.

It is completely feasible to understand computers (including algorithms) well enough to make an informed choice and buy a computer that will stick with you for a long time, the first time you buy. You just have to ignore the people who tell you you are too dumb to understand some aspect(s) of the computers, and be willing to spend a little time learning about the things you don't you know.

 

[Chavodel8en]

As for the OP: Buy any modern computer you like. If you start diving often, you may find a computer that you prefer and even regret your first purchase, but how would you know now. I used my 1997 puck computers until I started Nitrox almost 15 years later as an example. Another example is my daughter’s boyfriend. We had him purchase a very nice Oceanic ProPlus 3. Great computer except he is starting to go towards the technical environment. Who would have planned that one? He will still get a couple of good years out of it regardless. Once you have experience on your type of diving, then you will be in a better place to purchase the computer type you really want. Personally, buy based on the features you want now but manage the cost of it. I do not believe the algorithm is important until you know you want a particular style of diving and that comes from experience. My only complaint about some algorithms used are those that penalize you unduly. There are some computers that will, to my understanding, add a penalty if you surface too fast, miss a safety or deep stop, etc. I want one that will let me decide how to penalize myself.

I just don't understand the reasoning that because a new diver doesn't know what kind of diving they will be doing, and/or doesn't understand the ins and outs of dive profiles, NDLs, etc, etc, that it makes no sense for that new diver to consider a computer's conservatism/aggressiveness, because they may make a wrong choice.

Yes, its true they may make a mistaken choice that they will revise once they get more information.

However, if this new diver is to completely ignore conservative/aggressive issues -- well, then they are just as likley -- or IMO more likely -- to make a mistaken choice of computer that will not match their future dives or their future better understanding of dive profiles.

The first instance is an affirmative choice that turns out mistaken. The second example is no affirmative choice made at all, but still turns out to be mistaken. The end result is the same bad result - a computer that doesn't quite match a divers future diving.

However, I do think some new divers may consider a computer's conservativism/aggressiveness and make a correct choice. We should at least give them the opportunity to do so.

Im not saying that this should be the main thing a new diver should consider. Ease of use, how long the battery lasts, etc. etc. Each person should make their choice as to what is most important to them. For some, these issues will be unimportant or secondary. For me personally, cost is the main factor by a lot. But all things being equal, I want a computer that gives me the most bottom time and Im willing to accept the extra sliver of risk that comes with it. I don't know much about the science of diving, but I feel competent to make that decision based on my simple practical understanding. I believe there are many new divers who can make a similar choice, if given the basic information.

I bought an Oceanic Geo at a going out of business sale -- mainly bc it was greatly discounted. I didn't consider the aggressiveness of the computer at the time - it just wasn't on my radar. If there had been a Zoop on sale for a bit cheaper, I would have bought that. *Lucky* for me, the Geo is fairly liberal -- and that matches my needs. Had I bought the Zoop in ignorance -- well in retrospect, I would have wished someone had given me all the information, bc now I'd be missing those few precious minutes of bottom time.