Poll: GTR to include stops when one gas is active/on for Shearwater’s AI Teric & Perdix computers?

[guyharrisonphoto]

After over 1500 dives (95% no stop, 5% light deco, <15 minutes) in the last 16 years, I can confidently say that the Oceanic ATR is quite accurate.

I can say the same thing for my wife and I's Scubapro Galileos, with over 300 dives between us (they were my first AI computer). The notion that GTR cannot be calculated accurately including stops is just so wrong, as many manufactures over many different computer models do it just fine. There is no reason at all not to have this very valuable information displayed in OC Rec mode.

 

[guyharrisonphoto]

Don't think you got the point.. GTR to plan a dive? It doesn't make sense, because if you use the GTR you didn't planned the dive at all (and you're wrong from the start!).
It's more like this:

- I planned my dive and I know my times already;

A) I compare what I already know with what the computer is showing to me and they (approx) matches: great, I'm re-assured and I'm a happy diver;

B) I check what I already know and I compare it with my computer but the data are greatly different. It's time to review it.

B - 1) Well I'm right, the computer is wrong because the GTR sometime can be off due to many assumption;

B - 2) After all the computer may be right, looking at my profile I didn't respected the depth and the times of my plan because I was distracted by that siren and I don't have time to stay at this depth any longer, better to do my deco stops and not risk it.

This is the correct way of conducting a dive IMO, and this is what I do. And I do all the above already with the TTS, but I have to do some mental calculations to interpolate my SAC at deco stops with the TTS, I have a complex and costly computer, I would love that those calculation are performed for me in real time by it.

This is "my" story, and I believe none here would use it differently in an advance diving, and anyway we have a working brain to understand the difference between a real data and an estimated data.

I think your approach is sound, but I would make an observation. Your "planned" gas consumption is a pure estimate based on assumptions--most notably fixed SAC from the beginning to the end of the dive-- and does not take real conditions into account. GTR makes some of these same assumptions (you will ascend at the prescribed rate, do the stops for the specified time at the specified depth) but replaces the fixed-SAC assumption with gas consumption measurement during the dive. Due to the "real time" nature of the GTR calculation it will invariably be more accurate than your pre-dive estimates unless there is a substantial computer malfunction. Also, the GTR updates rapidly (every one or two minutes) and so can change its "assumptions" during the ascent and even during the stops to adjust for real-time gas consumption. It is more accurate in pretty much every way than a pre-dive gas plan, because it accounts for actual deviations from planned depths, increased (or decreased) workload during the dive, variations in ascent speed, in sum your actual SAC during all parts of the dive.

So, if I saw a big deviance between my pre-dive estimated gas plan, and my GTR, I would either follow the GTR or default to following the more conservative of the two for safety reasons. But, I would not assume the GTR is making "wrong" assumptions.

 

[Kermit98]

Potentially need another option: "Don't really care either way".

I have a SW Perdix AI, I use the GTR feature lightly. I wouldn't ever use it for planning, its just a nice neat little reminder/check of where I am in terms of gas remaining.

Personally I don't breath it down to zero GTR, if I am on a shallow little bimble dive then I tend to be coming up slowly, often inline with the bottom to < 10m so it very quickly becomes a large number anyway. If I am on a deeper dive I tend to have multiple gases (falling outside the OP question) so have a more structured plan and I am usually in deco.

It taking a minute or two off at depth to put 3mins on at 3-7m would be fine, but wouldn't lose sleep either way.

 

[Jay]

I've added a few more options to this poll as when the voting was even, the voting pattern seemed to be Res<->Yes versus Non-Rec<->No. This is mainly for new voters that might stumble across this post in the future when the question is inevitably raised again.

Thinking I was missing something from the non-Rec world, I asked about it on the Tec forum (link: Do any Tec-Rec (or light deco) divers use GTR?). The main upshot of that thread is that many didn't know what GTR was, and various comments highlighting the very Rec-orientated nature of GTR. Given that, it was interesting to see the no-vote double as a result of that poll, and once again those voters mainly being non-Rec.

 

[scubadada]

Anyone is allowed to go back and change or augment their vote. I went back and anwered the questions regarding type of diving and having an AI computer

 

[J-Vo]

I would like to display both tank pressures without GTR as it clutters the screen and is useless. A diver should know min gas for max depth + contingencies. It's simple, you get to that and you go up.

That said, if your going to do it for deco it should be calculating GTR to the first switch.

 

[Jay]

I would like to display both tank pressures without GTR as it clutters the screen and is useless. A diver should know min gas for max depth + contingencies. It's simple, you get to that and you go up.

GTR's an optional display.

For Tec, knowing that math is a given, I think we can probably guarantee that for typical Rec divers (not the SB crowd) probably the opposite is true.

That said, if your going to do it for deco it should be calculating GTR to the first switch

That too is a good idea, but probably (now) way put of the scope of this thread given the voting pattern for a Rec-based GTR change.

 

[Jay]

Clearly this poll has been a resounding success! NOT!

1400 views over 2 weeks, 40 votes in total, double the number of votes against than for, and just under half of (disclosed) Rec divers voting no. It must be one of the most successful polls in recent SB history ... make that unsuccessful!!
Seriously, with those stats the proposal is well and truly going no where.

In my mind I'll redefine GTR to be gas time to SS. That's a much smaller 'error' which 'works' for me.

Thanks to everyone who participated in this thread and poll.

(p.s. @RainPilot and @Joebar, you didn't vote for either of the first two options, but did for some other options - just FYI)

 

[Joebar]

I miss the button: "I don't have AI, so I don't care about GTR"

I used to have an Aladin AIR O2 with AI. There was a value called "Remaining Bottom Time". It included deco Stops but no safety stops (Safety stops weren't invented at this time). For me it was "dangerous" because I started to priorise RBT over tank pressure control.

 

[RainPilot]

(p.s. @RainPilot and @Joebar, you didn't vote for either of the first two options, but did for some other options - just FYI)

I didn’t, because I neither agree nor disagree. The way I use GTR would be unaffected by the proposed change. All I care about is knowing which method is implemented, then it becomes a distant third aid to gas planning.