Shearwater Perdix Computer Users running Open Circuit...question?

[PfcAJ]

What is ascent schedule in NDL diving? Deep stops? Safety stop at 5 or 3 meters? I can do all that without changing GF on my computer. OP was conservatism settings in rec mode, so I guess no deco. Max dive time can be agreed beforehand by comparing your plans, but I still don't need to change my computer settings to comply with dive plan, just remember when to go up.
Besides, ascent schedule is run by most conservative computer in a dive team. I will not change my GF to 100/100 to match you, but I will expect you to follow when I start up. I will do the same with a buddy that dives more conservative computer than I do.

All those things. The idea is to minimize surprise and the need to explain things underwater by having a dive plan.

So won't change your 100/100 but will follow the most conservative... you might as well change it if you're going to do it. This way the NDL display is the same and TTS is the same on both your and his computer. It all reduces ambiguity. No one gets smarter underwater.

 

[RayfromTX]

"No one gets smarter underwater."

Sir that is one of the wisest things I've ever heard about scuba diving.

 

[DevonDiver]

I am (and, to my reading of the latest posts, "some of us are") recognizing that there is a difference between actual risk incurred and the semi-arbitrary label of estimated conservatism displayed by a particular computer.

If we assume that the diver has some experience with the computer/algorithm, then we see more imperative behind conservatism settings.

For example, consider when a diver regularly dove with a specific models lowest conservatism setting... and had no physiological issues doing that.

But on some occasions that diver identifies that they're effected by known DCS pre-disposing factors. This is when increasing conservatism is a prudent measure to take.

Another diver might feel constant, unwarranted, post-dive fatigue when using zero conservatism on their computer. They might notice that increasing conservatism by one or two steps alleviates that fatigue.

That becomes their standard setting. If/when they identify further DCS predisposition on a given dive, they'd have to further increase their conservatism to compensate.

Does it really matter which computer or algorithm you dive?

I'd suggest what matters most is establishing your own individual baseline setting for your computer... and knowing to add appropriate conservatism when experience suggest that your susceptibility to DCS may have elevated.

I'd have no hesitation to increase conservatism to match a buddy/team. I wouldn't drop conservatism to match anyone else.

 

[Neilwood]

If we assume that the diver has some experience with the computer/algorithm, then we see more imperative behind conservatism settings.

For example, consider when a diver regularly dove with a specific models lowest conservatism setting... and had no physiological issues doing that.

But on some occasions that diver identifies that they're effected by known DCS pre-disposing factors. This is when increasing conservatism is a prudent measure to take.

Another diver might feel constant, unwarranted, post-dive fatigue when using zero conservatism on their computer. They might notice that increasing conservatism by one or two steps alleviates that fatigue.

That becomes their standard setting. If/when they identify further DCS predisposition on a given dive, they'd have to further increase their conservatism to compensate.

Does it really matter which computer or algorithm you dive?

I'd suggest what matters most is establishing your own individual baseline setting for your computer... and knowing to add appropriate conservatism when experience suggest that your susceptibility to DCS may have elevated.

I'd have no hesitation to increase conservatism to match a buddy/team. I wouldn't drop conservatism to match anyone else.

That to me is one of the best descriptions of how to select conservatism and/or GF that I have read. Clear and concise.

The only issue I can foresee with adjusting conservatism to suit another diver is by being talked in to going less conservative. Being more conservative tends towards safety, being talked in to going less conservative means the margin is narrowed.

There is really no point in trying to get 2 different computers running different algorithms (such as Buhlman and RGBM to agree - they are programmed on completely different assumptions). Just because 2 lines on graphs meet doesn't make them the same lines. Accept that they are different and accept that you will leave the water based on the most conservative. You might try to get them to agree by playing with settings for a particular set of circumstances but change those circumstances (ascent rate or profile for example) and one will give a different answer again.

 

[stuartv]

The only issue I can foresee with adjusting conservatism to suit another diver is by being talked in to going less conservative. Being more conservative tends towards safety, being talked in to going less conservative means the margin is narrowed.

Even that is a grey area. Some people think GF30/85 is more conservative. Others would say that GF50/80 is actually more conservative.

You could potentially get the same dichotomy even with a recreational computer that uses a proprietary algorithm and which only offers Conservatism settings of 0, +1, and +2. The manufacturer obviously thinks +1 is more conservative than 0. But, if you happen to exceed your NDL and +1 results in you staying deeper, longer, then is it really more conservative? Who can really say?

I guess the only area that seems pretty black-and-white is NDLs. If you're just doing "no deco" dives, than a setting that gives shorter NDLs is more conservative.

 

[admikar]

you might as well change it if you're going to do it.

There is really no point in trying to get 2 different computers running different algorithms (such as Buhlman and RGBM to agree - they are programmed on completely different assumptions). Just because 2 lines on graphs meet doesn't make them the same lines. Accept that they are different and accept that you will leave the water based on the most conservative.

I guess the only area that seems pretty black-and-white is NDLs. If you're just doing "no deco" dives, than a setting that gives shorter NDLs is more conservative.

Leaving aside which GF settings are really more conservative, my "refusal" to change is more eloquently said by @Neilwood .

 

[Bigeclipse]

I recently posted a similar question earlier. This post is geared to the setting used.
The Shearwater Perdix has 3 settings for NDL.
The Conservative options are Low, Med, High...

Who's running what...and why?
Thanks

my father and I have been running on low with no ill effects, however, on dives deeper than 60ft we have been doing 5 minute safety stops.

 

[geoff w]

If we assume that the diver has some experience with the computer/algorithm, then we see more imperative behind conservatism settings.

For example, consider when a diver regularly dove with a specific models lowest conservatism setting... and had no physiological issues doing that.

But on some occasions that diver identifies that they're effected by known DCS pre-disposing factors. This is when increasing conservatism is a prudent measure to take.

Another diver might feel constant, unwarranted, post-dive fatigue when using zero conservatism on their computer. They might notice that increasing conservatism by one or two steps alleviates that fatigue.

That becomes their standard setting. If/when they identify further DCS predisposition on a given dive, they'd have to further increase their conservatism to compensate.

Does it really matter which computer or algorithm you dive?

I'd suggest what matters most is establishing your own individual baseline setting for your computer... and knowing to add appropriate conservatism when experience suggest that your susceptibility to DCS may have elevated.

I'd have no hesitation to increase conservatism to match a buddy/team. I wouldn't drop conservatism to match anyone else.

When I started diving with my Petrel 2 a few years ago, I just left it on medium conservative in rec nitrox mode and everything was fine. Surprisingly, it was more conservative than my Suunto on the first dive in some cases, then the Suunto became much more conservative on subsequent dives of a repetitive dive series. Then I took an advanced wreck class in south Florida a couple of months ago and my thinking changed dramatically, in part because of everything we did as far as Shearwater settings during our ascent

Now, when I'm doing deeper (recreational) dives at home in colder water, I have it set to tec mode to use the default 30/70 setting. However, when I go on vacation to someplace warm and tropical with great viz and less thermal protection and weight needed, and less worries about current, I figure I will change to something more suitable for easy recreational fun diving, like the medium conservative setting in rec nitrox mode. Although if I have a few mai tais the night before on vacation, or if we're experiencing higher stress diving such as ripping current, bad viz, rough conditions causing seasickness, night dives, idiot dive operators, etc, I will probably set to a more conservative GF. The great thing is you can tailor conservatism to the conditions. If I run out of bottom time before everyone else because my computer and Dr Buehlman tells me so, I'll either ascend early or follow the model. There's only cause of DCS, and that's not doing enough decompression (per John Chatterton)