Computer Expert Question

[ronski101]

Last yr I got a 5 dive new reg which had a Tusa IQ-700 console computer. It's logarithm is much more restrictive in N2 absorbing than my wrist Aries Atmos1. Several times I have gone into DECO on the Tusa while the Aries was ok. What I want to do is reset the Tusa to about 26% O2 so that it will more closely match the Aries N2 absorbtion rate that i have used for years. The Tusa is always 1 bubble in N2 absorbtion rate ahead of the Aries which with a little math should be about 26% O2. Will this work? Have I forgotten something? I can't believe that I am the only one who has ever dove with 2 unmatching computers. Any qualified insight would be appreciated.

 

[j2s]

Down load the software 'V-Planner'...[30 day free trial] you can play around w/it and set whatever parameters you want....You'll be able to compare any dive computer to its' calculations.....Works w/oc, ccr and trimix.......I don't use any of my computer's guide lines [have 4 different brands]....I run the calculations for a dive manually, to keep in practice, then run V-Planner and write the times/depths on a wrist slate........I've found doing that to be more accurate........

 

[DuboisP]

maybe the Aries Atmos1 is not enough restrictive ?

 

[lowviz]

...//... Several times I have gone into DECO on the Tusa while the Aries was ok. ...//...

"Deco" can also mean that your 1-3 min "safety" stop is no longer optional. -my guess as to the computer mismatches. Also realize that this is a fuzzy estimate. It is saying that you are PROBABLY OK. You need to do better than that...

If you are going into deco with questions, you owe it to yourself to learn the basics first. This is the value of tables, start there.

---------- Post added December 6th, 2012 at 02:06 AM ----------

In addition, I would refer you to a recent expert in this field: http://www.scubaboard.com/forums/q-...do-i-cancel-my-certification.html#post6564236

 

[t-mac]

Probably better not to game the computer. Conservatism is generally more complicated than this and while under certain conditions you might get an approximation, this isn't a fix. The issue is the different algorithms. I've had the same issue with different algorithms and I've changed over to using two computers with the same algorithm. When you need that backup you don't want it bent, but you also want it to give you meaningful information so YOU don't get bent and so you don't have to go to those table and spend a lot of time on the boat while others dive.

 

[superspeed]

If your set on diving with both computers I would not mess with the PPo2 just to get them to match but rather dive them both and listen to which ever one tells you your at your NDL first and end the dive. Changing the gas selection to 26 is basically just throwing out anything valid that computer might be telling you, so why not just leave it off?

 

[g1138]

Put the Tusa into gauge mode. If your primary computer fails you're then planning off tables; assuming you're still on tables.
Don't push your computers. I personally like to being my ascent before I hit the 10min mark before deco, even then I rarely come close.

And no, you're not the only one to have dove mismatched computers.

 

[lowviz]

Even ascent rates can cause DC's to differ. http://www.scubaboard.com/forums/ad...3-dive-computer-ascent-rates.html#post5403555

 

[RonR]

The short answer is no, you won't get any useful approximation by changing the %O2 in one computer. The algorithm is going to vary depending on the depth, profile, previous dives, and other factors, and it's not a simple linear calculation. Does the Tusa have any adjustments to conservatism? If so, they would be designed to factor in all the variables, and you could tweak them.

You may be dealing with two computers that are tending towards opposite ends of the conservatism spectrum, but they might not be as far apart as it seems. Conservatism in dive computers is hard to nail down, but differences tend to seem more extreme in shallower, longer dives, because we treat deco/ no deco as an on/off function when in reality is is a gradually increasing slope, very gradually increasing at shallow depths. So on shallower dives even a slight divergence in the algorithm conservatism can translate into many minutes more or less of no-deco time. The same computers might show much less difference- in minutes of no-deco time- at deeper depths. Computers that show only a minute or two difference on a deep dive might diverge by many minutes on a shallow one. What you don't see on the shallow dive is that one is "almost" in deco, and the other is "barely" in deco. They may not be, in mathematical terms, very far apart at all, but because they treat deco/ no-deco and a binary switch, one seems much more conservative. If it were displayed in analog terms, as say a % of risk, they might not seem very different.

A lot of divers see going into deco as falling off a cliff. But it's a lot more like hikers ascending a very gradually increasing slope, and deciding at what % grade to turn back. If one person decides to turn back at 30% and another at 32% grade, and they both head straight uphill, they will turn around at almost the same time. If they instead traverse the slope at a very shallow angle, the 30% hiker may turn around a long time before the 32% hiker. His turnaround point is no more conservative than it was going straight uphill, his risk no greater, but the difference in minutes between the two is greater because they attacked the slope at a shallow angle.


There is a lot of discussion of computer conservatism in this thread: http://www.scubaboard.com/forums/co...2569-some-computers-unsafe-2.html#post6373034

Ron

 

[scubadada]

The less time you spend underwater, the less your risk of DCS. Is the DSAT algortihm unsafe, I don't think so. The Seiko algorithm is quiet conservative while the DSAT algorithm is reasonably liberal. I dive an Oceanic VT3 as my primary computer and an Oceanic Geo as my backup, both running DSAT. They run almost exactly the same NDL. My life is uncomplicated and I have a backup if my primary fails, along with my SPG on the 2nd HP port.

Best, Craig