Another computer quandary.

[Tony Carrozza]

True?

 

[scrane]

To me a computer that locks you out for any reason is like a speedometer that stops working if you go over the speed limit.

 

[stuartv]

To me a computer that locks you out for any reason is like a speedometer that stops working if you go over the speed limit.

Let's be clear. All this talk of computers that lock you out seems to be very misleading to some people. It is nothing like a speedometer that stops working. If anything, it's more like a GPS that displays your current speed and the posted speed limit. If you exceed the speed limit for long enough, it stops showing you the posted speed limit but still shows your current speed. Still not a perfect analogy, but much closer.

No computer that I know of "locks you out." What they do is lock you into Gauge mode (AKA Violation Gauge Mode, AKA VGM, in Oceanic terminology) for 24 to 48 hours. And, they don't do that until you have gotten out of the water and been out for some amount of time - say, 5 minutes or more. They don't do it during a dive.

Also, you can still dive with it, even in VGM. It will just limit you to what you can see/do in Gauge mode. I.e. it will show you depth and dive time. It just won't show you NDLs. You could still use it and dive based on tables.

And, it will only go into VGM if you have mandatory deco stops and you skip/ignore them. So, the fact that you CAN still use it in gauge mode, SHOULD be moot. If you had mandatory deco stops and you skipped/ignored them, you probably SHOULD stay out of the water for 24 to 48 hours.

At least, that is my specific experience with Oceanic and Hollis computers. I think other brands work in essentially the same way, but I could be wrong.

 

[scubadada]

@stuartv is correct

I've been diving Oceanic computers since 2002 nearly 1400 dives. I do mainly no-stop dives but about 5% are light deco. I have never been in violation gauge mode (VGM). If I ended up in VGM, I probably deserve to sit out for 24 hours

If you ascend above a deco stop for less than 5 minutes, descend and clear the stops, the computer continues to work normally. If you ascend above a deco stop for more than 5 minutes, you can still descend and clear the stops, but the computer goes into VGM and will work only as a gauge. A full 24 hour surface interval is required to return the computer to normal function.

There are two other ways to enter VGM besides ascending above a deco stop for more than 5 minutes, both are nearly inapplicable. If one has a deco stop below 60 ft or descends below 330 feet, the computer will go into VGM. The former has recently been discussed on SB and would require a really extraordinary dive, the latter, well...

Dive in a reasonably responsible manner and you will never have experience with VGM

 

[sabbe]

I accidentally got my backup TX1 into VGM mode when I did a gas switch only on my Perdix. Thankfully modeling with Multideco showed nitrogen loading was negligible day-to-day but the TX1 wanted full 24 hours, not the 22 hours the boat schedule allowed. I left the TX1 home day 2 to clear it, and it came back for the rest of the week.

Multiple dives in 1 day or heaver nitrogen loading and I would have been down to only 1 computer the rest of the trip. Lesson learned, keep diving 2 computers (+tables) in case I screw 1 up, selling the TX1 so I don't have to screw around with 2 different menu systems.

It would have been nice if the TX1 could continue calculations even after violated instead of a 24 hour timer. Staying in gauge mode for a week would have been really annoying.

Sam

 

[scubadada]

@sabbe

All entries into VGM are due to errors by the user, your's just happened to be more recoverable.

 

[Gareth J]

Fundamentally dive computers are running a mathematical model which is attempting to model gas saturation in the body during a dive - descent, bottom time, ascent (and surface interval).
The first thing to understand is that we DON"T really know what is happening.
A number of different models have been developed that, as long as you follow the individual model rules, it is expected to get you out of the water safely. No individual model will guarantee that you won't get a bend, it is just unlikely, i.e. a fraction of a percent.
(Bends - decompression illness, do occur even when you dive 'within the table' these are often referred to as undeserved bends, or in table bends).

If we fully understood what was happening, there would only be one model!
Also the existing models wouldn't have version number - VPM-B, VPM-C, gradient factors or other compensations / adjustments

So, if you 'break the rules' of the particular model your dive computer is using it is going to get confused, hopefully, it will attempt to give a 'best guess'. The VR3 (early mixed gas computer) was known for giving you the joyous message REVERT TO TABLE if you really did something stupid that it couldn't determine an exit strategy for. The upside was you new you where in trouble!

Small violations, repetitive dives with short surface intervals, yo yo'ing, missed stops, fast ascents etc are all violations of the majority of models. Early computers weren't that clever, and would lock you out for 24Hours. Modern computer have much more computing power, have padding and additional punishment for minor indiscretions, like adding safety stops, additional decompression stops, reducing no stop time etc.

In addition modern computers often attempt to compensate for other things it determines are risk factors, cold water diving, high gas consumption etc.

Just because you are using a dive computer does not means the 'rules' don't apply. Whilst we may not fully understand how the body is working. We do understand a number of factors that are considered aggressive (likely to increase the risk of a bend). If you keep this in mind during a dive, you are less likely to 'upset' your computer or give yourself an 'undeserved bend'.

I would far prefer to dive in an environment where compulsory decompression was considered normal, rather than a fixation with attempting to push every second out of a no-stop dive, which is a very aggressive practice. Those doing decompression diving have an expectation that they will need to have good decompression protocols and ascent practice, and will generally pad their stops on the ascent if they have been aggressive during the dive.

Regardless of your dive computer, understand what is good dive practice will improve your safety and reduce the risk of you getting an 'in table bend'.


Gareth

 

[BRT]

To me a computer that locks you out for any reason is like a speedometer that stops working if you go over the speed limit.

If the computer cannot calculate a way to get you out of where you are it will have to lock you out. If you skip a deco stop the computer would have to assume you are bent or close to it. What other option does it have than to quit trying to calculate?

 

[rongoodman]

If the computer cannot calculate a way to get you out of where you are it will have to lock you out. If you skip a deco stop the computer would have to assume you are bent or close to it. What other option does it have than to quit trying to calculate?

Shearwater and Liquivision just continue their calculations, taking into account the missed stops, and warn you that you screwed up. There's no reason for them to throw up their hands and quit, so they don't.

 

[BRT]

Shearwater and Liquivision just continue their calculations, taking into account the missed stops, and warn you that you screwed up. There's no reason for them to throw up their hands and quit, so they don't.

What do they tell you to do?