Safety stop feature request

[tursiops]

To me, I’m not in deco until I have exceeded m-value.

CW, this is the problem. You are confounding "being in deco" for your body with "being in deco" for your computer. If you set the Perdix to 75/75, of course it will show deco if you get to 76% of the m-value. But by your definition, you are not REALLY in deco until you hit 100% of the m-value. You really can't have it both ways......your Teric is showing 99% of the m-value, your Perdix is showing 75% of the m-value.

It is like the old days when people learned about deco diving by wearing two computers, one set to air, one to Nitrox, which was the gas they were actually using. They watched the air computer for their dive, and it went iknt "deco," and they learned to follow the instructions on that computer to learn what it showed and how to hold stops, etc. But since they were on Nitrox, they were never really in deco.....it is just that the air computer thought they were.

Your Perdix at 75/75 thinks you are in deco. Why is this a problem? You TOLD it to say that!

 

[scubadada]

...I have no aversion to the term deco. To me, I’m not in deco until I have exceeded the 100% m-value. If I have not exceeded the 100% m-value, the computer should not tell me that I’m in deco.

IFTFY. Really?

 

[CWK]

So, if you plan a Deco Dive you use 99/99 as GF Setting?

I plan a no deco dive to surface gf of 99, and do a 3 min safety stop and that would be perfectly acceptable as a no deco dive because my Teric has the rec mode settings that allows me to do that. But that 3 min safety stop, given the right dive, may only reduce my surface gf to 92 which would still be high.

What I am saying is that I want to plan a no deco dive to surface gf of 99, and do a safety stop and that takes my surface gf to, say, 75 and have my computer tell me how long that safety stop would be.

 

[CWK]

CW, this is the problem. You are confounding "being in deco" for your body with "being in deco" for your computer. If you set the Perdix to 75/75, of course it will show deco if you get to 76% of the m-value. But by your definition, you are not REALLY in deco until you hit 100% of the m-value. You really can't have it both ways......your Teric is showing 99% of the m-value, your Perdix is showing 75% of the m-value.

It is like the old days when people learned about deco diving by wearing two computers, one set to air, one to Nitrox, which was the gas they were actually using. They watched the air computer for their dive, and it went iknt "deco," and they learned to follow the instructions on that computer to learn what it showed and how to hold stops, etc. But since they were on Nitrox, they were never really in deco.....it is just that the air computer thought they were.

Your Perdix at 75/75 thinks you are in deco. Why is this a problem? You TOLD it to say that!

Mel,

Move away from tec diving and think about recreational diving. I’m not talking about deco diving.

There are 2 completey different settings that I am trying to get to.

Firstly, NDL. I would like to set NDL to m-value.

Secondly, safety stop. I would like to set safety stop in terms of surface gf (say 75) and have the computer tell me how long that safety stop will be.

 

[NAM001]

Very few recreational computer use Buhlmann, so they can't do GFs.

i CANT ATTEST TO HOW MANY COMPUTERS USE BUHLMAN, oops but the principle should be able to be implemented with what ever method is used. I refer to the computer telling you when it is safe to surface by means of live data and not the blanket 3 or 5 minute rule system. I would suspect that any computer knows if you will exceed limits should you surface. I suppose that SS alerts on computers are there not for the purpose of real safety rather than for the what if safety. IMO it is time to toss the what if stuff and exchange it for real data results. the computer can do the temp thing in NDL or SS calculations, or have min conservatism hard coded to the equal of GF90 for surfacing or use the actual adjustable conservative settings. It would amount to all dives being a deco dive and the only stop would be SS whether for 10 seconds or 10 minutes. Yes rec dives means that you can ascend to the surface directly. I cant say how may times I have been asked about ,,,, If rec dives require no stops........ why the safety stop (too many have no clue that there are factors that cannot be measured and used for calculating,,, there fore no understanding of the SS.).......and then why does the computer assume the worst case and call for a safety stop on every dive. why is the safety stop the same whether you do a 10 minute dive or a 30 minute dive. That follows up with like the 60 ft dive limit. If it is just a recommendation why cant I just skip it,,, since it is not mandatory, all together and set the computer to ignore SS alarms etc. Couple that with,,,,,,,,,,If a little conservatism is good then a lot is a lot more better. There is a giant gap in what divers do not know about computers. The idea of being able to have the best of all worlds has become the social norm. you cant have long NDL's and the highest safety conservatism at the same time. I really wish agencies would make a computer course or add it to AOW. As it is,,, we give newbies very expensive tools, that they neither dont know how to use or have a desire to understand. I suspect that the first time most divers ever use more than the normal screen it is when they get into nitrox and have to nav the menus to change FO2 for the first time, Perhaps nitrox is the FIRST time they have ever used the menu's because they took it out of the box and dove it as is. That sounds a bit crazy but ask a number of auto drivers and asn them do they have insurance. they say yea then ask them what their deductable is. they have no clue. If we are going to toss dive tables and go to computers, then lets do it all the way and get rid of the, square profile, rule of thumbs and demand computer makers follow suit. Then teach table use as a backup means for a failed computer or lack of a computer.

 

[NAM001]

Two points:

* Can the boat tell you were in deco for a /75 setting after you get out?
* Why does the boat ask that you don’t go into deco?

Can’t you just be honest with everyone and do a deco dive? If the boat really will not allow it, is that short hand for longer dives not being allowed? Or hanging about on a blob for 15 minutes not being allowed?

Hi Ken could that be perhaps the liability coverage of the boat. or maybe tec dives requires more equipment larger quantities of equipment to be carried onboard such as O2. the only thing that makes sense is that if you were set your computer to be very conservative and stayed down to long for that conservatism setting would the boat be asking if you have a computer that is functioning for the next dive and not locked out? It may be similar to boats asking to see you max depth for the dive. the boat has eh dive plans premade and the in and out of the water is based on those schedules for economy and moving form site to site. boat attitudes on things vary greatly.

 

[NAM001]

For the last 2 years I have been diving recreational with:
1. Teric on my left wrist set to Rec mode 99/99
2. Perdix on my right wrist set to Tec mode 75/75

For all recreational dives, my Teric on my left wrist has never showed that I was in deco because I have never exceeded m-value. For quite a few dives, Perdix on my right wrist has showed that I am in deco even though I have not exceeded m-value. It is not correct that Perdix is showing that I am in deco just because my surface gf has reached 76. It cannot be that my left hand is never in deco, whereas my right hand sometimes is. The error is that Perdix shows deco when m-value has not been exceeded. Am I prepared to routinely surface when my Perdix shows that I am in deco because my surface gf is 76? Absolutely! Am I prepared to routinely surface when my Perdix shows that I am in deco and my surface gf is 85. Yes, I am because I am not in deco. My preference is to offgas until my surface gf is 75 or less. To me, this is an extremely conservative setting. I can use a more aggressive setting for recreational diving, but that is not my preference.

Recreational diving is non deco diving. Computers can incorrectly showing deco when gf high is exceeded but not m-value. This does not matter in tec diving because m-value will be exceeded shortly after gf high is exceeded, but is an error in recreational diving where m-value is not exceeded.

that is the problem with using conservatism settings like 75/75. the gf hi controls the NDL calculation and ultimately if you follow the NDL calc you should be albe to non stop to teh surface and not exceed surf GF of 75.. deco means that you exceeded NDL and nothing more. because of that you can not directly go to the surface and hit the surface with gf hi 75 or less so you need to stop and off load prior to surfacing to achieve that parameter you called for it to do. the conservatism setting like you used of 76/76 should eliminate totally any need for a SS . Its another on of my beefs about how computers are used you use a 75/75 and still want to do a 3-5 minute SS. it is redundant. IMO the 3-5 minute stop should only be considered doing if you are diving 99/99. those that do both probably do so because they dont have GF or equivilant data to view and if one safety measure if good than 2 is better for safety. I doubt that most people under stand the inter relationship consequences of their computer settings.

 

[NAM001]

Very few recreational computer use Buhlmann, so they can't do GFs.

here is a article regarding algorythms used. Buhlmann is quite popular according to this article and is used often as a blend with others. of course that does not prohibit RGBM comprising of 90% of the market sales leaving Buhlmann the minority one. It just shows that perhaps over half of the makers use it one way or the other.

Dive Computer Algorithms For Dummies

 

[tursiops]

here is a article regarding algorythms used. Buhlmann is quite popular according to this article and is used often as a blend with others. of course that does not prohibit RGBM comprising of 90% of the market sales leaving Buhlmann the minority one. It just shows that perhaps over half of the makers use it one way or the other.

Dive Computer Algorithms For Dummies

I'm sure Scubadada will provide more info, but that article is quite misleading. The PZ+ and ScubaPro implementations of Buhlmann have undocumented and proprietary modifications of Buhlmann. The more correct statement is that almost no manufacturers other than Garmin and Shearwater use Buhlmann such that you know what you are getting. Anybody else uses the name as a marketing gimmick more than an explanation.

 

[wstorms]

Firstly, NDL. I would like to set NDL to m-value.

Secondly, safety stop. I would like to set safety stop in terms of surface gf (say 75) and have the computer tell me how long that safety stop will be.

So if I understand you correctly, you want a countdown to a chosen Surf GF?
But what I don't really understand is what you want to accomplish with that in real life? If you set 99/99 as GF, your NDL will be determined accordingly. If I understand you correctly you are now looking for the optimum safety stop?

Since you want to do recreational dives (no mandatory stops), I'm going to assume 40 meter as a depth limit. If I play with SubSurface and use a 40 meter square profile on air (gf 99/99) I get a max NDL of 10 minutes (10 minutes and 10 seconds puts you in deco). If you ascent in 3,5 minutes (let's call that 4) to 5 meter, you arrive at SS depth with a Surf GF of 92%. When you do your traditional safety stop (3 minutes, 5 meter), you have a surf GF of 73%.
If you really want to go at 75%, you can go to the surface 10 seconds earlier....
Seems like a lot of hassle (and risk of user error) to lengthen your dive with less than 2 minutes in total, just to not break the boat rules.