Suggestions for getting my first dive computer

[KenGordon]

Do you have an adjustable Conservatism Factor? Do you set it to its highest value? If you don't, are you really being as safe as you can? If you don't, how do you, personally, decide that the amount you are safer is enough, but more conservatism is not required?

When you set your computer to be "more conservative", are you decreasing your changes of DCS from 2% to 1%? From 0.2% to 0.15%? To borrow an earlier poster's analogy, how do you know whether you have moved from 1m away from the precipice to 2m away, or if you have moved from 1km from the precipice to 2km away?

I'm sincerely NOT trying to bash you or make light of how you choose to set your personal boundaries. I AM trying to highlight that it seems like some people are very quick to bash others for diving a "liberal" computer to its NDL while lauding others who choose a "conservative" computer, and yet none of us has any evidence to present that shows that one is truly any more effective at preventing DCS than the other. From the evidence that I'm aware of, these differences seem to be closer to the 1km vs 2km example than the 1m vs 2m example. I would love to see actual data on the subject, if anyone has any.

I have posted examples for people falling off your cliff from distances you'd call miles previously. Read the incident reports. Hang out at a chamber.

All the decompression algorithms use devolved gas as a limit. They all increase dissolved gas with time and depth. So they all model increased time or depth as increased risk. Maybe all the models are wrong and the longer you stay at depth the safer you are?

 

[Centrals]

Do you have an adjustable Conservatism Factor? Do you set it to its highest value? If you don't, are you really being as safe as you can? If you don't, how do you, personally, decide that the amount you are safer is enough, but more conservatism is not required?

When you set your computer to be "more conservative", are you decreasing your changes of DCS from 2% to 1%? From 0.2% to 0.15%? To borrow an earlier poster's analogy, how do you know whether you have moved from 1m away from the precipice to 2m away, or if you have moved from 1km from the precipice to 2km away?

My 18 yrs old Uwatec Aladin Pro Nitrox has NO Conservatism Factor and the O2 setting is in 2% increment! And I am still DCS FREE(touch wood) after thousand of dives and sometimes 5 dives per day.
To be honest I have no idea what algorithm that Aladin used and I don't really care.
Do you know any dive computer that provide DCS FREE algorithm?

 

[stuartv]

I have posted examples for people falling off your cliff from distances you'd call miles previously.

Right. You can get bent using even a really "conservative" computer. So, is that the computer? Or other factors? In which case, does it really matter if you use a conservative or liberal computer?

My 18 yrs old Uwatec Aladin Pro Nitrox has NO Conservatism Factor and the O2 setting is in 2% increment! And I am still DCS FREE(touch wood) after thousand of dives and sometimes 5 dives per day.
To be honest I have no idea what algorithm that Aladin used and I don't really care.
Do you know any dive computer that provide DCS FREE algorithm?

No, I don't. Do you know of any that have data to show they have more or less incidence of DCS that others?

 

[Centrals]

No, I don't. Do you know of any that have data to show they have more or less incidence of DCS that others?

As far as I know only one of the Uwatec Aladin model was found to be faulty over last 20yrs.
Divers still got the "hit" even diving well within the limit. WHY?
So a Mares Puck at US$150.00 is as safe as a Shearwater Perdix II at $800.00!

 

[KenGordon]

Right. You can get bent using even a really "conservative" computer. So, is that the computer? Or other factors? In which case, does it really matter if you use a conservative or liberal computer?

Another point I was making earlier in the thread is that the algorithm is not an important 'feature' when it comes to a new diver buying a computer because that diver will probably find that other factors limit the dive before the computer.

 

[KenGordon]

As far as I know only one of the Uwatec Aladin model was found to be faulty over last 20yrs.
Divers still got the "hit" even diving well within the limit. WHY?
So a Mares Puck at US$150.00 is as safe as a Shearwater Perdix II at $800.00!

The mares puck is likely to be safer having fewer ways for an uninformed user to ask it to do something more risky.

Also, since there is no planner for the Shearwater it is hard to figure out if it does anything other than the simple disolved gas modelling in the face of different profiles and doing so would be counter to the claim that is uses Buhlmann ZHL16 with GF. The Puck manual says that it gets more conservative with repetitive diving, multi day diving and reverse profiles. An informed user could do the same with the GF computer, but we are talking about new divers here.

Another way to look at the different risks is that the $650 difference could be spent on training in how to perform deco dives safely with the Puck. Round here you can do the course with the man who wrote the book for that money.

At the risk of sounding like some old fashioned DIR fanatic, there is no magic in the computer. Your body does the dive and longer NDLs on the computer make no difference to how your body deals with the nitrogen, changing the computer to a more liberal one does not 'allow' anything. For a given profile you will get bent or not regardless of which computer you take.

 

[stuartv]

As far as I know only one of the Uwatec Aladin model was found to be faulty over last 20yrs.
Divers still got the "hit" even diving well within the limit. WHY?
So a Mares Puck at US$150.00 is as safe as a Shearwater Perdix II at $800.00!

Do you have any evidence that either one is safer than the other?

I bought a Perdix AI and I had no thought whatsoever that my need for it was for increased safety from the deco model it uses.

The highest GF the Perdix AI will let you use is in Tec mode, and that is GF99. In Rec mode, it's GF95. In me experience, that puts it very, very close to what DSAT produces on recreational computers. So, pending actual data to change my mind, I'd say neither (the Puck or Perdix) is any more dangerous than the other.

Another point I was making earlier in the thread is that the algorithm is not an important 'feature' when it comes to a new diver buying a computer because that diver will probably find that other factors limit the dive before the computer.

So, a new diver should buy a computer with the idea that once they are no longer a "new" diver, they'll probably buy another computer?

Anyway, just because you may have taken a long time to get to where you could stay down long enough to be limited by NDL does not mean that anything like "most" people are like that. I was consistently limited by my NDL (using Nitrox and a liberal computer) within 6 months of getting OW certification. And my SAC is nothing special. Lots of "new" divers have a SAC as good or better than mine. I completely disagree with your statement that [new divers] "will probably find that other factors limit the dive before the computer." But, my disagreement is based on my feeling that anyone with less than 50 dives could legitimately be regarded as a "new" diver. If you're talking about people with less than 10 dives since OW, okay, maybe. But, why would you recommend someone buy a computer just based on the needs of their first 10 dives?

The mares puck is likely to be safer having fewer ways for an uninformed user to ask it to do something more risky.

Also, since there is no planner for the Shearwater it is hard to figure out if it does anything other than the simple disolved gas modelling in the face of different profiles and doing so would be counter to the claim that is uses Buhlmann ZHL16 with GF. The Puck manual says that it gets more conservative with repetitive diving, multi day diving and reverse profiles. An informed user could do the same with the GF computer, but we are talking about new divers here.

Another way to look at the different risks is that the $650 difference could be spent on training in how to perform deco dives safely with the Puck. Round here you can do the course with the man who wrote the book for that money.

How is the Puck safer again? With a Petrel/Perdix, even if you put it in Tec mode, the highest GF setting you can possibly set it to still only makes it behave (for recreational dives) pretty much just like a rec computer running DSAT. Do you have any data to support the idea that a DSAT computer produces a higher risk of DCS than a Puck?

What do you mean there is no planner for a Shearwater? You can download Subsurface for free and plan away. Or are you suggesting that maybe Shearwater doesn't use a strict Buhlmann w/GF implementation and, instead, maybe has something proprietary in their algorithm implementation that makes it not behave just like any number of plannings applications (e.g. Subsurface, Mult Deco, etc.) work?

Yes, you could spend the extra money on training - and then be certified for deco and not have a computer that is good for deco....

I'm not saying the OP (or anyone else) SHOULD buy a Shearwater (unless the person knows they want AI and are interested in tech diving - then I AM saying they should buy a Perdix AI). I'm just saying that I don't see any facts to support your statements, which seem to be trying to assert that a new diver would be safer with a Puck than with a Shearwater computer.

 

[Chavodel8en]

Another point I was making earlier in the thread is that the algorithm is not an important 'feature' when it comes to a new diver buying a computer because that diver will probably find that other factors limit the dive before the computer.

Yes, as a new diver, I didn't come close to reaching NDLs. But (checks log), within 3 years, after 60 dives & AOW, my computer was cutting short 2 wreck dives in Oahu. And that was a more aggressive Oceanic computer, it would have been even less time w other computers.

So everyone should just buy a "starter" computer, but may need to replace it after a few years (or a few months as in stuartv's case above) if they bought a conservative computer and they discover it doesn't fit their diving preferences?

A better (and more economical) strategy IMO would be to buy a starter computer that I wont need to replace bc it fits my preferences.

As a new diver I would have been able to process all the information and decide that a more aggressive computer would be the best choice for me. I believe that new divers can process basic information and decide if aggressiveness/conservatism matters to them.

I still have this computer, and Im glad that its "aggressive". Its limited my bottom time on a couple other occasions - always on a vacation wreck dive, which are special dives for me where I want maximum bottom time.

 

[dmaziuk]

Yes, as a new diver, I didn't come close to reaching NDLs. But (checks log), within 3 years, after 60 dives & AOW, my computer was cutting short 2 wreck dives in Oahu. And that was a more aggressive Oceanic computer, it would have been even less time w other computers.

Yeah... Love your profile pic, too. So very apropos.

 

[KenGordon]

Do you have any evidence that either one is safer than the other?

How is the Puck safer again? With a Petrel/Perdix, even if you put it in Tec mode, the highest GF setting you can possibly set it to still only makes it behave (for recreational dives) pretty much just like a rec computer running DSAT. Do you have any data to support the idea that a DSAT computer produces a higher risk of DCS than a Puck?

A GF computer which allowes a 95/95 setting is more aggressive than a Puck i think you will agree. Part of that means that it has a longer NDL time for any given depth. Do you deny that a longer time at a given depth is riskier than a shorter time?

Clearly nobody has done a comparative study of GF computers and Pucks. So of course I have no data, just the principles on which these models are based.