buying a new dive computer

[scubadada]

Here is the orphaned (entire product line discontinued but still supported and warrantied by Oceanic) Aeris equivalent of the VEO 3.0 for $199.

http://www.amazon.com/Aeris-Compute...TF8&qid=1453718082&sr=8-1&keywords=Aeris+a300

The Oceanic (and the now discontinued Aeris line) offer a dual Algorithm option on many of their more recent computers, this IMO is an big advantage. While not as precise and user adjustable as a top end unit with Gradient Factors it does allow for a simple selections of 'liberal' (DSAT) or 'conservative' (PZ+). For myself with the warm water low stress drift dives in Cozumel, NDL becomes an issue and I like using the DSAT algorithm. The PZ+ algorithm is available if I wished to change to a less liberal algorithm.

Both the DSAT (basis for PADI RDP) and PZ+ (a Buhlmann ZHL-16C variant) algorithms also have an additional conservative factor if the base algorithm is too liberal for you or you are trying to closely match the NDLs of another computer running a more conservative algorithm. You can make a liberal computer more conservative, there's nothing you can do with a computer running an algorithm that you find too conservative. Sometimes, flexibility is the key

 

[dmaziuk]

In practice the "strictly recreational" DSAT is available on oceanics and your choices are veo, geo, or vtx. Every other "recreational" DC including cobalt runs some kind of RGBM. (Well, there's also the odd one out DG03 that runs some kind of Buhlmann "modified to include deep stops".)

I believe consumers should make informed decisions, in this case, a basic understanding of decompression algorithms is a part of that process

Basic understanding of decompression algorithms for simple recreational dives is a) they none of them get you bent and b) come up progressively slower as you get shallower and take longer breaks between the dives if you're doing repetitive diving for several days.

 

[stuartv]

In practice the "strictly recreational" DSAT is available on oceanics and your choices are veo, geo, or vtx. Every other "recreational" DC including cobalt runs some kind of RGBM. (Well, there's also the odd one out DG03 that runs some kind of Buhlmann "modified to include deep stops".)

I do not believe that is correct. See this thread that I linked before. Lots of manufacturers have something other than RGBM.

http://www.scubaboard.com/community/threads/so-you-want-to-buy-a-new-computer.305374/

Basic understanding of decompression algorithms for simple recreational dives is a) they none of them get you bent and b) come up progressively slower as you get shallower and take longer breaks between the dives if you're doing repetitive diving for several days.

That is borderline insulting. I bought my first computer shortly after I got my OW certification. Did I research computers, including their algorithms? Yes. Did I have a deep understanding of decompression theory when I was done? No. And it's not necessary. Even someone with no math/physics/chemistry background can understand lab test reports that show that computers with one type of algorithm generally give longer NDLs, and the differences get greater as you do more dives in one day, versus others that use a different algorithm.

I bought an Oceanic computer (an Atom, BTW, which also has dual algorithms and wasn't in your list). My g/f has a Cressi Giotto. Mine consistently allows longer NDLs, even though she OFTEN chooses to swim 5 feet or so above where I am, to extend her NDL and gas. And even when I'd only been diving 7 months (i.e. last summer), I was normally staying down right up to my NDL and still coming up with 900 psi to 1200 psi left in my tank. So, to ME, the extra minutes of NDL are helpful and I am very glad I did the research on algorithms before I purchased.

I think the many posts I see that tell new divers not to worry about algorithms because they will be limited by gas long before they are limited by NDL are a serious disservice to those divers. Posts like that are encouraging people to buy computers based on how they dive today, at the base of the steepest part of their learning curve, instead of how they could be diving in 6 months or a year.

Why should anyone be encouraged to buy a computer that they might legitimately want to replace (because of its algorithm) in a year? There is no reason they can't buy a computer today that will still be serving them well in 5 years or more. And in 5 years, most anyone that dives even a few times per year could have a gas consumption rate that improves enough for a conservative computer to become restrictive to them.

 

[boulderjohn]

I think the many posts I see that tell new divers not to worry about algorithms because they will be limited by gas long before they are limited by NDL are a serious disservice to those divers. Posts like that are encouraging people to buy computers based on how they dive today, at the base of the steepest part of their learning curve, instead of how they could be diving in 6 months or a year.

Many new divers start off with excellent SAC rates. I certified two friends a few years ago. The husband's was pretty close to mine when we did the OW checkout dives, and the wife was way better than both of us on those checkout dives. When I have a smaller, athletic female in a class, I assume she is going to do better than I right from the start.

 

[dmaziuk]

I do not believe that is correct. See this thread that I linked before. Lots of manufacturers have something other than RGBM.

Not in the sub-$200 range. In the sub-$200 range your options are oceanic's dsat/pz+ or zoop/puck/leonardo/"no product matching selection" deep6: all rgbm. Algorithm choices start in the $800+ range.

I bought an Oceanic computer (an Atom, BTW, which also has dual algorithms and wasn't in your list). My g/f has a Cressi Giotto. Mine consistently allows longer NDLs, even though she OFTEN chooses to swim 5 feet or so above where I am, to extend her NDL and gas. And even when I'd only been diving 7 months (i.e. last summer), I was normally staying down right up to my NDL and still coming up with 900 psi to 1200 psi left in my tank. So, to ME, the extra minutes of NDL are helpful and I am very glad I did the research on algorithms before I purchased.

This is why I said "define simple dives". If my "simple dives" took me all the way to NDL and I had the gas for it, I'd do the deco course, buy a tech. computer, and plan my dives as deco dives. No problem. I believe the course would include algorithms and why I should buy a computer running Buhlmann with user-settable GFs.

As far as longer NDLs, I've seen that claim repeated many times, usually in the "zoop too conservative" form, but I've only seen one table with actual numbers so far. As I recall the largest difference was up to whooping 5 minutes. Personally I don't care about 5 minutes, if the site is that great I'll get another tank and go back down there. YMMV of course.

PS.

Why should anyone be encouraged to buy a computer that they might legitimately want to replace (because of its algorithm) in a year?

Because, to mis-quote another poster, the computer you'll want to buy in a year is likely not the computer you're going to buy today. (Also because most people don't from DD to full tech in one year -- but you knew that.)

 

[stuartv]

If my "simple dives" took me all the way to NDL and I had the gas for it, I'd do the deco course, buy a tech. computer, and plan my dives as deco dives.

Even if you decide to be conservative and only stay down until your NDL says 5 minutes, a computer with 3 extra minutes of NDL is still 3 more minutes of bottom time.

boulderjohn pointed out that even some brand new divers have a SAC that will let them dive to their NDL. Are you really suggesting a brand new diver who is NDL-limited should just go ahead and take AN/DP? I think not. So, if your response is, "if they're a new diver, I would tell them to be conservative and not stay down anywhere close to their NDL." Okay, fine. As I said, if the NDL is 5 minutes longer, they still get to stay down 5 minutes longer, no matter what margin of conservatism they elect to use.

As far as longer NDLs, I've seen that claim repeated many times, usually in the "zoop too conservative" form, but I've only seen one table with actual numbers so far. As I recall the largest difference was up to whooping 5 minutes. Personally I don't care about 5 minutes, if the site is that great I'll get another tank and go back down there. YMMV of course.

I have posted links many times and they are in the thread that I linked earlier. One example (of several): The lab reports shows a 3rd dive where, after an elapsed dive time of 36 minutes, one computer is showing an NDL of 56 minutes and another computer is showing 2 minutes. Those are the two extremes at that time, in that test. But, if you look at all the data, there are a lot of computers with a lot of NDL left and several others with a lot less NDL left.

If you choose not to look at the data that debunks your statements....

Because, to mis-quote another poster, the computer you'll want to buy in a year is likely not the computer you're going to buy today. (Also because most people don't from DD to full tech in one year -- but you knew that.)

And that happens so often because...? People follow the Scubanati advice and buy a computer without regard to algorithm and then figure out a year later that they want something less conservative?

I did not follow the Scubanati advice. I bought a computer where an algorithm that would give me longer NDLs was a factor in my decision (the advice being to not count that as a factor in my purchasing decision), and that same computer is still, today, over 1 year later, my top choice of computers to dive with. The fact that I have started to pursue tech diving and that computer works perfectly well as a backup for tech diving is simply gravy. I have an Atom 3.0, a SeaBear H3 and a Petrel 2. And right now, today, if I were going to do a Recreational/sport (i.e. NDL) dive and for some reason I were only going to take 1 computer in the water with me (say, I left the Petrel at home and someone I was with forgot their computer and needed to borrow one), I would dive the Atom and loan the H3.

To paraphrase the Scubanati on BCDs, "buy your second computer first."

 

[dmaziuk]

I have posted links many times and they are in the thread that I linked earlier. One example (of several): The lab reports shows a 3rd dive where, after an elapsed dive time of 36 minutes, one computer is showing an NDL of 56 minutes and another computer is showing 2 minutes.

Yes, and both are showing >60 minutes 5 minutes later and 8 metres shallower. That means what, exactly?

 

[stuartv]

Yes, and both are showing >60 minutes 5 minutes later and 8 metres shallower. That means what, exactly?

That means that if you are ending your dive on a reef that is 40 feet deep, you will end your dive a lot sooner with the one than the other.

 

[stuartv]

ps. As I said earlier, that was just one example. Different algorithms don't usually make a big difference on the 1st dive after a long surface interval (but they do make a small difference). But, as you do more dives in a day, the different algorithms CAN (but don't always) make a big difference. Are you really still trying to argue this point?

 

[scubadada]

Stuart, thanks for taking over the attempt at educating dmaziuk, I had given up. Though believing he/she knows everything, posts say otherwise. One of the dangers of the internet, separating the wheat from the chaff

I have a feeling that this thread is not helping ohdot any longer