New Shearwater Dive Modes.

[MyBuddy]

I would never rely much on some prediction based on what it assumes I will do. If this is true, maybe there should be a prediction setting, DYNAMIC to calculate stops and TTS based on assumed switches, STATIC to calculate based on current gas. Or show the two one above the other in different colors.

Well you should just stop diving now because even the algorithms in dive computers, dive planners, tables, etc. are making assumptions that your tissues will on gas and off gas at certain rates based on your depth and the gases you’re telling it your breathing.

There’s lots of assumptions made of how you will perform when you’re planning a dive. Best practice is to plan your dive and dive your plan, so nothing your computer tells you during the dive should be a surprise.

Your computer is also not just making assumptions willy-nilly to get your deco stops and TTS. You’re programing the computer with the gasses you are planning to breathe and will have with you, the highest PPO2 you’d accept for the dive and deco, and many other parameters. (This is why divers should be intimately familiar with their computer’s features and how the values are calculated. If you put bad information in you’ll get bad information out.) The computer then takes all the preferences and values you’ve programmed in and your actual dive profile up to that point in the dive and gives you the minimum amount of Deco and TTS. TTS being the time it would take you to arrive at the surface with the GF you selected if you left for the surface at that instant in the dive and traveled at 30fpm to the first stop or the surface.

If you want the worst case scenario when having to deco on backgas, turn your deco gasses off. When you get to a stop switch to the appropriate gas and turn it on/switch to it on the computer. It will then recalculate based on you breathing that gas all the way to the surface. I don’t think this would be the best approach but you could do it.

And isn't what you said also true for overhead environments? The TTS is assuming recreational - that you can begin your ascent now. It has no idea that you are 100' in a cave or wreck and can't ascend for another 5 or 10 minutes.

This statement is absurd. Of course a dive computer’s TTS can’t calculate a physical overhead. No reasonable person would ever expect it to. Shearwater clearly explains how TTS is calculated in the manual. The physical overhead would be accounted for during your dive planning. The job of the TTS is calculate how long it will take you to get to the surface including vertical travel time and time spent with a virtual overhead. TTS is useful in recreational dives but it’s essential in technical diving. You have to still use your head to interpret the data presented by the computer, what’s going on in the environment you’ve chosen to explore, and what is your dive plan in order to make decisions.

 

[MyBuddy]

But as I noted: That said, in these cases I am planning no-stop dives so I am not concerned.

So all I care about is my remaining gas time. TTS is for intents and purposes meaningless.

I’m not sure if there was an edit while I was responding to your other post or if I didn’t quote all of your post by mistake, but yes for NDL dives TTS is less important. Though not all together meaningless, as you should keep your TTS less than your GTR.

 

[ReefHound]

You have to still use your head to interpret the data presented by the computer, what’s going on in the environment you’ve chosen to explore, and what is your dive plan in order to make decisions.

"I would never rely much on some prediction based on what it assumes I will do. "

Is that not essentially what I said?

 

[Tracy]

I would never rely much on some prediction based on what it assumes I will do. If this is true, maybe there should be a prediction setting, DYNAMIC to calculate stops and TTS based on assumed switches, STATIC to calculate based on current gas. Or show the two one above the other in different colors.

That is exactly how it works, it predicts that you will make the stops and gas switches that make most sense. It already has that function, if you don't want it to do that, you would use the computer as designed and not turn on gases that you don't have.
You are using it in a 3 gas mode and complaining that it works as designed. If you want it to base calculations off one gas, you have options, you can continue using three gas mode and turn off the other gases or you can use plain ol nitrox mode. Both of those things will do what you want.

 

[ReefHound]

That is exactly how it works, it predicts that you will make the stops and gas switches that make most sense. It already has that function, if you don't want it to do that, you would use the computer as designed and not turn on gases that you don't have.
You are using it in a 3 gas mode and complaining that it works as designed. If you want it to base calculations off one gas, you have options, you can continue using three gas mode and turn off the other gases or you can use plain ol nitrox mode. Both of those things will do what you want.

I'm not talking about predictive planning but NDL. And I want to be able to switch in water if I jump with the wrong setting.

 

[inquis]

Though not all together meaningless, as you should keep your TTS less than your GTR.

That's not at all mandatory. You would have a point if GTR assumed an ascent, but that's not how it works. GTR is calculated at the current consumption rate. If nonzero at the current depth, it will increase, perhaps dramatically, upon ascent.

Additionally, GTR (at least on Shearwater devices) is the time until the pressure that YOU configure. It's common to use GTR as a countdown to do "something", which is initiated when it reaches ZERO. For example, start the ascent at your Minimum Gas threshold, turn around and start back toward the anchor line, etc.

 

[J-Vo]

Shearwater added these modes because they need to compete with the other manufacturers feature lists. It's all about the recreational diver that is comparison shopping.

 

[Joneill]

If you are not deco diving there are no stop times. I don't think the person with 36/32/21 and using it as convenient way to switch between the most popular rec options is going into deco.

If folks are too lazy to turn off it gases that they are not using, maybe they need a new hobby? It literally only takes a few seconds to do so why would anyone want to leave a gas turned “on” if they are not carrying/using it?

 

[inquis]

One man's "lazy" is another man's "efficiency".

 

[Pavao]

Shearwater added these modes because they need to compete with the other manufacturers feature lists. It's all about the recreational diver that is comparison shopping.

Right, complete bs in my opinion, the way they were was some of the things that set them apart from the rest, now air mode, nitrox mode, 3 gas nitrox mode… wtf, where is this going?

It is still the best dive computer in the market, as far as the operation as a dive computer goes, but depending what version you look at, I think there are others I’d chose personally.
The fanaticism is strong here and I open myself up to the bombardment that is to follow for saying such things, if it helps easy your pain, I won’t use anything else when I tech dive, either CC or OC