Disabled deco gas on backup computer.

[rhwestfall]

wouldn't you do that calculation as part of the predive planning anyway? so you should know you can deco on your back gas ( or at least some sort of team share) as long as you have a TP for you back gas the deco gas is an extra margin of redundancy

I do, but also have the luxury of real time conditions with my old computer running as a back-up.....

 

[lermontov]

I do, but also have the luxury of real time conditions with my old computer running as a back-up.....

yes you do but wouldn't it be great if the DC had that information on screen so that the TTS was the correct time on the active gas - it seems both the OP and your methods are trying to compensate for what i see as a pretty simple (?) software solution

 

[Zi55ou]

I suppose it would be nice if the comp could show it. But given all the information it already displays it could easily become cluttered.

Like rhwestfall says the calcs are done for a worst case scenario but during the dive having an ability to quickly see what the immediate consequences of that scenario is useful. E.g. I have planned for a maximum time of one hour of deco on my back gas should I lose my deco, but I'm getting cold my air deco is at 30min and I've seen about as much as I want to see so let's head up now. This is never going to extend your dive beyond what you would have worst case scenario'd for just shorten it and increase your awareness of the consequences of a failure that hopefully/likely not happen, but one that you've already planned for.

 

[lermontov]

I suppose it would be nice if the comp could show it. But given all the information it already displays it could easily become cluttered.

Like rhwestfall says the calcs are done for a worst case scenario but during the dive having an ability to quickly see what the immediate consequences of that scenario is useful. E.g. I have planned for a maximum time of one hour of deco on my back gas should I lose my deco, but I'm getting cold my air deco is at 30min and I've seen about as much as I want to see so let's head up now. This is never going to extend your dive beyond what you would have worst case scenario'd for just shorten it and increase your awareness of the consequences of a failure that hopefully/likely not happen, but one that you've already planned for.

not sure what DC you have but the shearwater has the option of removing information on the main screen if you find it cluttered - I completely understand the ideas behind what you and @rhwestfall are doing and don't disagree - i just wish the TTS was really the TTS based on the active gas not the gas that you plan to use ( or not) I have a back up DC set on different G/f -but that's another topic

 

[Zi55ou]

not sure what DC you have but the shearwater has the option of removing information on the main screen if you find it cluttered - I completely understand the ideas behind what you and @rhwestfall are doing and don't disagree - i just wish the TTS was really the TTS based on the active gas not the gas that you plan to use ( or not) I have a back up DC set on different G/f -but that's another topic

Apologies if I misunderstood, seems like we only have one option, more dive computers! (Anyone wanna donate a teric, perdix, ostc or three?)

 

[ChuckP]

This is wrong, TTS(Time to surface) is calculated just on the gasses that are turned on.

Also on Shearwaters you don't have to turn a gas on to select it, you can directly choose a gas that is turned off. The TTS will change accordingly as you now have turned on another gas.

Good to know, maybe I misunderstood where I heard that at - I still like having only gasses that I have with me entered in the computer, good way to review computer anyways.

 

[electric_diver]

Nitek HE dive computers were like this. I used one for about a decade. Your deco time showing was assuming that you continued to breath the current gas. It was always a relief to see approximately 60 minutes of air deco drop to about 20 minutes of O2 deco when I did the gas switch at 20 feet.

Shearwaters were the first that I used that gave you a time to surface that assumed all optimal gas switches from all programmed gasses were done.

 

[J-Vo]

Interesting discussion as I just this morning sent a message to Shearwater.

One of my Perdixs shows TTS based on all gases programmed, and the other shows it based on current selected gas only. Once I get on O2 they both sync up. I think it's nice having both, but as far as I can tell from the manual the second one is doing something it should not. This worries me that there may be other bugs in the unit.

 

[RyanT]

This worries me that there may be other bugs in the unit.

.

Please follow up when you hear back from Shearwater, I'm interested in what they say.

 

[Diver-Drex]

From the Perdx manual, page 48 - “Off gasses are not used in decompression calculations.”

I run one of my two Perdix with only back gas on as is being discussed here.