Decisions on a Dive Computer

[Belzelbub]

So if you are diving in a less than planned way the knobs on the Shearwater let you make stuff up as you go along.

No knobs, just some buttons.
But, yeah, I wouldn’t advocate for anyone changing the GFs during the dive. However, knowing your current (or estimate in a few minutes) m-value number is good information.

is that what you want millions of people doing? Or do they need an absolute line to conform to? If the only thing making some of them pay attention to their computer is the prospect of sitting out a day then is that bad?

If they need that absolute line, they have no business diving near the NDL, and probably no business diving as well. If the prospect of a lockout is all that prevents them from making an ill advised dive, then they have poor impulse control. I wouldn’t want to be diving in the same group as those divers. They may still choose to dive anyway in gauge mode. Dumb? Yes, but they paid for the day, so they want to do the dives.

My issue with the lockout is that it is arbitrary. Exceeding NDL for a few seconds on a conservative setting is quite different than blowing way past the m line. Yet both would yield the same punishment. A knowledgeable diver can use the information available to make a decision on what to do in either of those cases. The tissue graph, for instance can help them decide if it’s a sit out for a bit, or chamber time situation.

 

[KenGordon]

If they need that absolute line, they have no business diving near the NDL, and probably no business diving as well. If the prospect of a lockout is all that prevents them from making an ill advised dive, then they have poor impulse control. I wouldn’t want to be diving in the same group as those divers. They may still choose to dive anyway in gauge mode. Dumb? Yes, but they paid for the day, so they want to do the dives.

You are describing the product of mass training and vacation diving. That is how it is.

My issue with the lockout is that it is arbitrary. Exceeding NDL for a few seconds on a conservative setting is quite different than blowing way past the m line. Yet both would yield the same punishment. A knowledgeable diver can use the information available to make a decision on what to do in either of those cases. The tissue graph, for instance can help them decide if it’s a sit out for a bit, or chamber time situation.

That is not what happens. What happens is that you need to have deco owing and surface (strictly be above stop depth for 3 minutes). If you go a couple of minutes over NDL you will have a minute of stops. To bend the computer you will have to ignore even doing a safety stop. This is exactly blowing past the m value line.

A knowledgable diver can decide whether to bend the computer, for example if the alternative is having nothing to breath, or wait a while at stop depth after the stops to reduce the chances of a bend. A knowledgeable dive knows to avoid saw tooth profiles, fast ascents, short surface intervals and to add conservatism for multiple dives over multiple days. The problem is not knowledgeable divers but ones who learn quickly, don’t dive often or are not interested in the minutiae of decompression theory.

When did anyone look at a tissue graph to decide whether to stay down? The actual useful innovation is Surf GF. Even that is just “interesting to know”. Chose a GF, dive it, maybe add 3 or 5 minutes of safety stop if the circumstances call for it, magically your Shearwater can decide that for you. The Suunto will also choose 3 or 4 minutes depending.

 

[Wibble]

Obviously we’re discussing two different algorithms: RGBM (reduced gradient bubble model) which one assumes isn’t Haldanian.

For Bulhmann+GF, truncating the final stop merely results in an increased GF-hi, a minute or two may finish at 50:82. In other words what most would consider perfectly safe.

The proprietary RGBM would use some unknown algorithm that’s maybe not as flexible as the more 'open' ZHL16+GF mathematical model.

In any case, Suunto probably follow the CYA principle and to hell with usability and the inconvenience it causes.

 

[scubadada]

...A knowledgeable dive knows to avoid saw tooth profiles, fast ascents, short surface intervals and to add conservatism for multiple dives over multiple days. The problem is not knowledgeable divers but ones who learn quickly, don’t dive often or are not interested in the minutiae of decompression theory.

When did anyone look at a tissue graph to decide whether to stay down? The actual useful innovation is Surf GF. Even that is just “interesting to know”. Chose a GF, dive it, maybe add 3 or 5 minutes of safety stop if the circumstances call for it, magically your Shearwater can decide that for you...

My friend @KenGordon

The more I dive my Teric, the more I appreciate its simplicity and flexibility. Most all of my dives are no stop, about 5% are light back gas deco. Dive profile, saw tooth, ascent violations, short SIs, even reverse profiles are most likely no longer on the list of violations, as long as they are accounted for by the computer, and taken into account for the current and subsequent dives.

When you dive a Shearwater computer set at a chosen GF high, you will not violate that value, as long as you make a normal direct ascent at 33 ft/min. Any safety stop you make will only decrease your surfacing GF. I find the SurfGF function very useful for dives close to NDL or for light deco. It allows me to adjust the SS or the last deco stop to surface with a GF I choose, less than my GF high

 

[rongoodman]

The proprietary RGBM would use some unknown algorithm that’s maybe not as flexible as the more 'open' ZHL16+GF mathematical model.

It isn't necessarily the bubble algorithm that's the problem, but Suunto's implementation. Liquivision computers ran VPM without playing those games.

 

[KenGordon]

Obviously we’re discussing two different algorithms: RGBM (reduced gradient bubble model) which one assumes isn’t Haldanian.

Suunto RGBM is a 9 tissue dissolved gas model.

In any case, Suunto probably follow the CYA principle and to hell with usability and the inconvenience it causes.

it doesn’t cause usability issues or inconvenience. It is not CYA, just an obvious incentive to follow instructions rather than learning the hard way.

 

[Centrals]

All over the real world there are people diving Suuntos and having a fine time.

One of the most popular brand in rec diving!

Algorithm means nothing to most beginning divers. If they were given Suunto in their initial training, chances are they will consider that for their next purchase.

 

[scubadada]

One of the most popular brand in rec diving!

Algorithm means nothing to most beginning divers. If they were given Suunto in their initial training, chances are they will consider that for their next purchase.

And it will not interfere with their diving, ignorance is bliss.

 

[Centrals]

And it will not interfere with their diving, ignorance is bliss.

What is wrong of using Sunnto for diving?
How many divers can explain or even know the algorithm of the dive computer that they used?
I can happily use one for multi-dive over multi-day.

 

[Swedinsidemount]

The best entry-level computer i think is the Mares Nemo 2 ($200). It is non AI but it can handle mulit-gas dives, and gives LOTS decompression info...its easy to use with gloves, mine was very durable and followed me for many years. I miss it's complex yet easy to read numbers and graphs...I moved on to a shear water peregrine and am looking to get a perdix/teric AI soon, but for those first few years the Nemo was AMAZING....p.s. i personally like analog spg's more