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mrmccoy
07-09-2009, 22:09
I have been looking at dive computers alot recently but would like to know some of the more liberal computers. I know that Suunto is one of the more conservative brands. The computer I do decide on will be nitrox compatable....that is the only thing set in stone.

neogeo
07-09-2009, 22:15
Most top dollar computers such as Suunto can be adjusted... I know you can adjust the conservativeness of some Suunto computers such as the D9

CompuDude
07-09-2009, 22:35
Suunto can be made more conservative, but at it's least conservative setting it's far more conservative than other models at their default settings. Mares uses the same (or similar) algorithm... very conservative.

ScubaPro/Uwatec is somewhat middle of the road.

Pelagic computers such as those from Oceanic/Aeris are the most liberal.

Most computers can be made more conservative, but few can be made more liberal.

mrmccoy
07-09-2009, 22:43
What about sherwood computers?

PTAaron
07-09-2009, 22:58
How big of a difference are we talking about?

Comparing the NDLs given by my Oceanic Geo and my PADI tables only shows a few minute difference at the most.

I'm curious, because my wife and I have Geos and we got a Mares for her father (good sale price at ST) ... I haven't had a chance to see what his base NDLs are yet. I'm sure with us all being new divers air will limit us before nitrogen loading, but I'm curious.

mrmccoy
07-09-2009, 23:13
How big of a difference are we talking about?

Comparing the NDLs given by my Oceanic Geo and my PADI tables only shows a few minute difference at the most.

I'm curious, because my wife and I have Geos and we got a Mares for her father (good sale price at ST) ... I haven't had a chance to see what his base NDLs are yet. I'm sure with us all being new divers air will limit us before nitrogen loading, but I'm curious.

Yeah air will probly be my limit for a while but i'm thinking about the future so I don't NEED to buy another computer for a while.

IndyDiver
07-09-2009, 23:21
What about sherwood computers?

The Sherwood uses the same Haldane/Spencer Algorithm as the Oceanic/Aeris/Pelagic computers do. It is liberal as far as computers go and used PADI/DSAT dive tables to validate its test data. The algorithm is based entirely on a tissue saturation model.

The Suunto, Zeagle, Mares computers all use a Reduced Gradient Bubble Model (RGBM) developed by Wienke, which tries to model bubble formation as well as tissue saturation. As Compudude says, they are the most conservative.

In the middle are the Scubapro/Uwatec computers that use a Bühlmann ZH-L8 ADT or Bühlmann ZH-L8 /MB(Micro Bubble) Algorithm. The MB is basically a Buhlmann tissue saturation model that has been modified to include deeper stops to try to control bubble growth. But, unlike the RGBM algorithm, it does not try to actually model bubble growth and reduction. These computers also have the most adjustment range. They can be made to be only slightly more conservative than the Pelagic model, or can be cranked down to be even more conservative that the RGBM computers.

IndyDiver
07-09-2009, 23:29
How big of a difference are we talking about?

Comparing the NDLs given by my Oceanic Geo and my PADI tables only shows a few minute difference at the most.

I'm curious, because my wife and I have Geos and we got a Mares for her father (good sale price at ST) ... I haven't had a chance to see what his base NDLs are yet. I'm sure with us all being new divers air will limit us before nitrogen loading, but I'm curious.

There is almost no difference between an Oceanic and a Uwatec on a single dive. However, the Uwantec will penalize your nitrogen loading for rapid ascents and the AI models will reduce your NDL times if you are consuming a lot of gas (equating it to exertion).

There is only a slight difference between the Oceanic and the RGBM computers (Mares is one) on a single dive, but on repetative dives the RGBM computers become more and more conservative in relation to the Oceanic computers. On a third dive the NDL time can differ by 10 or 15 minutes depending on the depth and length of the dives.

PTAaron
07-09-2009, 23:46
How big of a difference are we talking about?

Comparing the NDLs given by my Oceanic Geo and my PADI tables only shows a few minute difference at the most.

I'm curious, because my wife and I have Geos and we got a Mares for her father (good sale price at ST) ... I haven't had a chance to see what his base NDLs are yet. I'm sure with us all being new divers air will limit us before nitrogen loading, but I'm curious.

There is almost no difference between an Oceanic and a Uwatec on a single dive. However, the Uwantec will penalize your nitrogen loading for rapid ascents and the AI models will reduce your NDL times if you are consuming a lot of gas (equating it to exertion).

There is only a slight difference between the Oceanic and the RGBM computers (Mares is one) on a single dive, but on repetative dives the RGBM computers become more and more conservative in relation to the Oceanic computers. On a third dive the NDL time can differ by 10 or 15 minutes depending on the depth and length of the dives.
Wow... that is pretty significant!
How will a "conservative" computer stack up against good 'ol tables on repetitive dives?

Sorry to slightly hijack the thread...

mrmccoy
07-10-2009, 00:30
Wow... that is pretty significant!
How will a "conservative" computer stack up against good 'ol tables on repetitive dives?

Sorry to slightly hijack the thread...

You have me wondering now!

IndyDiver
07-10-2009, 06:57
This page: http://www.scubadiving.com/gear/dive has reviews that discusse the results from diving different computers and which ones are conservative and which ones are liberal. They used to have the charts from the chamber tests online, but those links are broken now.

There is also this page: http://www.missionscuba.com/other-scuba/dive-table-comparison.htm which has a comparison chart. Notice the time range at each depth for the Suunto computer (RGBM). The higher numbers are from the first dive and the lower numbers is where it goes to with repeat dives.

PTAaron
07-10-2009, 08:08
Thanks for the info!

I wish we could have talked the father in-law into spending the extra $80 for a Geo... oh well! We'll make due ;)

SlvrDragon50
07-10-2009, 10:18
Compudude said Mares are conservative; however, that table lops Mares in the same group as the liberal Oceanic and Aeris.

Could someone clear this up?

BubblesMcCoy
07-10-2009, 10:41
How big of a difference are we talking about?

Comparing the NDLs given by my Oceanic Geo and my PADI tables only shows a few minute difference at the most.

I'm curious, because my wife and I have Geos and we got a Mares for her father (good sale price at ST) ... I haven't had a chance to see what his base NDLs are yet. I'm sure with us all being new divers air will limit us before nitrogen loading, but I'm curious.

There is almost no difference between an Oceanic and a Uwatec on a single dive. However, the Uwantec will penalize your nitrogen loading for rapid ascents and the AI models will reduce your NDL times if you are consuming a lot of gas (equating it to exertion).

There is only a slight difference between the Oceanic and the RGBM computers (Mares is one) on a single dive, but on repetative dives the RGBM computers become more and more conservative in relation to the Oceanic computers. On a third dive the NDL time can differ by 10 or 15 minutes depending on the depth and length of the dives.


My dive buddy uses an Oceanic Veo while I use a Mares M2. Even after repetitive diving to depths of around 80' (at altitude), the computed NDL difference between his computer and mine was barely noticeable. After three days of repetitive diving, air consumption, rather than NDL, was the bottom line for us.

If you are an experienced diver going to greater depths for longer, I can imagine that the difference would be more noticeable. Rather than base a decision solely, or even largely, on conservativism, I would find a computer that has the features you want and is intuitive to you. Just a suggestion.

Also, if downloading the data is important to you, be sure to check into cable/method that each computer uses. I love my M2, but downloading via the antiquated infrared serial system is truly a pita.

CompuDude
07-10-2009, 12:56
Compudude said Mares are conservative; however, that table lops Mares in the same group as the liberal Oceanic and Aeris.

Could someone clear this up?

Different models may use different algorithms. The model lineup changes over time. I believe Mares is now using a similar RGBM variant to Suunto, which puts them squarely in the conservative group. It's possible I'm remembering wrong, but I don't think so. If they're using a Mares computer that is Pelagic-based, like the Oceanics, etc., then it's true that they would be quite liberal.

I'd be curious to know which model Mares computer was used for that table... and how long that table has been around.

Edit: I just double-checked the Mares website (http://www.mares.com/product_detail.php?id=394&region=USA). All of their current computers are using RGBM now. This either wasn't always the case, or that table (http://www.missionscuba.com/other-scuba/dive-table-comparison.htm) is just plain wrong.

Some good info here: Dive Computer Secrets Revealed | Scuba Diving Magazine (http://www.scubadiving.com/gear/2006/10/dive-computer-secrets-revealed) and here: Crunching the Numbers | Scuba Diving Magazine (http://www.scubadiving.com/gear/2006/10/crunching-the-numbers)

CompuDude
07-10-2009, 13:02
Wow... that is pretty significant!
How will a "conservative" computer stack up against good 'ol tables on repetitive dives?

Sorry to slightly hijack the thread...

Tables will almost always lose to a computer, in terms of allowed bottom time, simply because they don't account for multi-level profiles that almost all real-world dives use.

That said.

For a truly square profile dive, such as one where you follow an anchor line down to a wreck, swim around that wreck at a fairly consistent depth, and then ascend immediately afterwards, IF you hit the tables precisely so you're not having to round up, I would guess that the more conservative computers would actually give you a little less time than the tables.

The so-called "liberal" computers are based on the same algorithm that PADI's tables are based on. It's the multi-level aspects that gets you more time with the computers, credit for time spent shallower, etc.

I've never tried to run numbers for repetitive dives to see how computers (in a square profile dive) stack up against tables. Again, though, considering the conservative computers get much more conservative the more repetitive diving you do (especially compared to liberal computers... again, which are based on the same Buhlmann tables), I would have to guess that the tables would still give you more time than the liberal computer. This assumes a truly square profile, however, and matching the table exactly so no rounding is needed, which is a nearly impossible to achieve in the real world.

Edit: The table (http://www.missionscuba.com/other-scuba/dive-table-comparison.htm) linked by IndyDiver above shows the NDLs (single dive, so comparison is not complete) for tables and Pelagic computers. You'll notice that they mesh up pretty darned closely. Compared to the other two columns, which deliver significantly shorter time limits.

CompuDude
07-10-2009, 13:14
My dive buddy uses an Oceanic Veo while I use a Mares M2. Even after repetitive diving to depths of around 80' (at altitude), the computed NDL difference between his computer and mine was barely noticeable. After three days of repetitive diving, air consumption, rather than NDL, was the bottom line for us.

If you are an experienced diver going to greater depths for longer, I can imagine that the difference would be more noticeable. Rather than base a decision solely, or even largely, on conservativism, I would find a computer that has the features you want and is intuitive to you. Just a suggestion.

This is good advice, and a good point.

A newer diver is far less likely to come across the NDL limits of any dive computer, liberal or conservative. Far more likely they will be air-supply-limited.

And the differences between models are not always blatantly apparent. It all depends on the exact profiles and which computer credits what, how, the gas mix used, etc. It IS possible to come out with fairly similar limits among various computers. It's also quite possible to come out with wildly different limits. I have a regular (highly experienced) dive buddy, and on one of our regular dives it's not uncommon for us to pick up a couple minutes of deco. (This usually clears before we get to the point of doing a deco stop, and we're well equipped to handle it regardless, so no comments, please.) He used to dive a Suunto, now he dives an Oceanic. There were a number of many occasions where I was cleared to get out (after we both made the exact same dive) and he had 8 minutes or so of deco remaining. After he bought the Oceanic computer and retired the Suunto, I'm usually the one stuck waiting a couple of minutes, after he's been cleared to get out.

Frankly, the best advice I can offer is this: Find out what your dive buddies are using (if you have regular dive buddies), and if they're going to be keeping that computer for a while. Everyone is happier when they're computers all mesh up, and no one has to wait for another computer to clear. That's best accomplished by matching algorithms/brands.

All that said, personally, I would rather set a liberal more conservative, if I was worried, than be annoyed that I can't set a conservative computer more liberal. Suunto and Mares make good computers, but I would buy Oceanic or Uwatec every time before buying Suunto. (That said, I do own a used Gekko that I picked up as a spare/loaner that has served me well on the few occasions I've used it, and has served a rather large number of friends well also! I wish I had a spare Uwatec instead, however, to better match up with my computer's limits.)

IndyDiver
07-10-2009, 15:01
Compudude said Mares are conservative; however, that table lops Mares in the same group as the liberal Oceanic and Aeris.

Could someone clear this up?

Different models may use different algorithms. The model lineup changes over time. I believe Mares is now using a similar RGBM variant to Suunto, which puts them squarely in the conservative group. It's possible I'm remembering wrong, but I don't think so. If they're using a Mares computer that is Pelagic-based, like the Oceanics, etc., then it's true that they would be quite liberal.

I'd be curious to know which model Mares computer was used for that table... and how long that table has been around.

Edit: I just double-checked the Mares website (http://www.mares.com/product_detail.php?id=394&region=USA). All of their current computers are using RGBM now. This either wasn't always the case, or that table (http://www.missionscuba.com/other-scuba/dive-table-comparison.htm) is just plain wrong.

Some good info here: Dive Computer Secrets Revealed | Scuba Diving Magazine (http://www.scubadiving.com/gear/2006/10/dive-computer-secrets-revealed) and here: Crunching the Numbers | Scuba Diving Magazine (http://www.scubadiving.com/gear/2006/10/crunching-the-numbers)

The older Mares used a Modified Haldanian Algorithm so they should be very close to the Pelagic based Oceanics. The newer ones are indeed all RGBM based.

I know the table is a few years old, but I am not sure exactly how old. The Mares data does not seem to be for its RGBM model.

mrmccoy
07-10-2009, 19:45
WOW I didn't realize how many different Algorithm's there were on the market! I never thought about having the same computer as a dive buddy or like computer. Thanks for all the info CompuDude and IndyDiver!

I'm sure gas will be my limiting factor for a while but I would like a computer that I can grow with. I'm still torn between wrist or console.

PTAaron
07-10-2009, 21:00
WOW I didn't realize how many different Algorithm's there were on the market! I never thought about having the same computer as a dive buddy or like computer. Thanks for all the info CompuDude and IndyDiver!

I'm sure gas will be my limiting factor for a while but I would like a computer that I can grow with. I'm still torn between wrist or console.
Being a newbie myself, and only having used a wrist computer I can say that I REALLY like it. It is easy to look bring up and keep an eye on when making your ascent - while you are venting your BC your wrist is right there near your face anyway.
I find it easier to look at my wrist than to pull up my console when I am checking depth.

Again... I've not used a console computer - so take that for what it is worth.

mrmccoy
07-10-2009, 21:24
That makes sense not having to hold a console up vs. just looking at your wrist. The Geo is one that I have been eyeing up too..........hummmmm

PTAaron
07-10-2009, 21:26
That makes sense not having to hold a console up vs. just looking at your wrist. The Geo is one that I have been eyeing up too..........hummmmm
Heck of a deal over on ST right now if you don't mind having "last years" color. I know for $200 savings, I sure as heck don't mind!

mrmccoy
07-10-2009, 21:32
I'm stuck between buying a reg., octo., and gauge OR a wrist computer. I figure I can rent a reg. untill I decide on what I want and just have a wrist mount computer.

navyhmc
07-10-2009, 21:48
I use a Geo, I will say you can't go wrong with it.

PTAaron
07-10-2009, 21:50
I'm stuck between buying a reg., octo., and gauge OR a wrist computer. I figure I can rent a reg. untill I decide on what I want and just have a wrist mount computer.
I must not have hit "submit" when I typed this earlier...

My wife and I got our Geos before we got our even did our open water certs, then saved up for the rest of our gear.