I recently changed my OSTC 3+ to the new firmware (V3.01) and now I am questioning how/when the dive computer displays the hint that I should change the gas?
I think this is called: quick gas change (better diluent)
Background: in the first dive it showed at 5 meters to switch to my Nitrox 53!
AT home I used simulation multiple times and found out:
Only if in ppO2 Setting Max and Max Deco are at 1.6 bar the warning appears when expected - at 20 Meters
If I change ppO2 Max to 1.5 than in last simulation it showed me to change at 10 Meters?!
For sure not relying on the display but want to understand how it works at it seems the the gas change hint come to late?
the OSTC constantly looks if there is a better gas (and better diluent, if in CCR / pSCR mode). If there is one, it generates the change advice. When in CCR/pSCR mode, it keeps the better gas aka best bailout gas in its pocket and puts the cursor on it once you enter bailout gas selection menu.
The best gas / best diluent is the one with its change depth shallowest of all but still deeper or equal to your current depth. Additionally, it must fit into your ppO2 max setting. The gases / diluents of type 'First' and 'Travel' (dubbed 'Normal' with diluents) are considered always in the search. The gases of type 'Deco' are included into the search once you arrive at your first stop.
At the same time you arrive at the first stop, the ppO2 max threshold switches from the normal ppO2 max to the ppO2 max deco, which puts the deco gases into reach in case their change depths are set on a MOD determined by the deco ppO2 max (which is normally the case). So opposite to older firmware versions, the threshold switch is not only triggered by picking a deco gas, but by arriving at a stop depth, too. This was done in support for CCR diving where there is no user-initiated gas switch to cue the OSTC for deco mode. Still, a manual switch to a deco gas will also make the threshold switch, so you will not get an ppO2 alarm when e.g. switching to Nx50 at 21 meters while your scheduled stop is at only 15 meters.
I have only done one deep dive since the upgrade (and since then my computer has had a depth sensor fail and is on the way back to Germany), but it did NOT offer the change to 100% at 7 m like I programmed it too. In fact, I realised that the indicated deco did not take this into account. Once I changed, the deco dropped dramatically.
After the dive I checked to make sure I had set the computer up alright, I had. Perhaps this needs looking at.
Well, you can't have the OSTC giving you a change cue at 7 meters for 100% as that would yield a ppO2 of 1.7 and the ppO2 max deco can only be set to 1.6 at max. So the cue will come at 6 meters or shallower, depending on ppO2 max deco.
The deco forecast will take the 100% into account, given that above mentioned conditions are met on the depth that is set as last stop depth. If last stop depth is set to 6 meters but a ppO2 max deco of 1.5 is set, the 100% will not yet be allowed on 6 meters and as 6 meters are the last stop, it will not be taken into account at all.
Anyhow, whatever has been set up with the gases and warning thresholds for deco prediction, the as-of-now data (stop depth, ceiling, CNS now) are always calculated based on the O2 and He % of the gas that is currently selected and hence shown in the lower left. Even if you are on the way to kill yourself by selecting e.g. 100% at 20 meters...
Ralph
PS: inside the pressure sensor, there is a silicon grease pocket that protects the metallic measurement membrane. This grease is factory fitted with the sensor manufacturer and can't be serviced. It has a habit of being eaten away or eaten through by salt water after long exposure. So to enlonger the life of the sensor, thorough rinsing of the OSTC in fresh water from time to time helps, even better with the backside coverplate removed to have better access for the fresh water to the sensor.
Did I understood this correct: the gas switch suggestion will come at the first next stop and not at the deco gas adjusted max. Depth? So if I carry the NX50 that I would usually switch to on 21m in order to reduce my saturation, and the first stop is scheduled at for example 15m, the OSTC would suggest the gas change at 15m and not at 21? If this is the case, than the OSTC probably also calculates the deco plan in the simulator according to the new rules?
I had this case today, OC, air and NX50, I was awaiting a best gas suggestion on 21m but nothing came, so I changed the gas manually...
Not really an advantage to the previous firmware version, for me it looks more like disadvantage.
- first stop at 15m, gas change cue at 15m on a deco dive -> yes, and will calculate that way, too. Going from 21 to 15 meters takes some 40 seconds. From decompression point of view it doesn't make a difference if you switch 40 seconds earlier or later, but if you stop at 21 meters to make the switch it will do for a bit - to the negative side. Switching on the fly may bring marginal benefit in this scenario, but i doubt feasibility of switching gas and changing the computer setting all while going through 21 meters while on constant ascent.
- in general: When diving, never fall behind the computer, i.e. have the computer to tell you what to do! It's your decision when to breath what, and _you_ have to take that decision.
- if you are on an extended multi gas dive (opposite to a deco dive with bounce profile), set your gases as travel instead of deco and you will get cues on any change possibility, including while decent phases.
For your last question, the answer is probably in the above text.
Sorry, but I don‘t agree with your theory. Changing from Air to NX50 on 21 m and remaining there for 3 Minutes after the change means reduction of the partial pressure of nitrogen from 2.449 bar to 1,55 bar. So even if some slow tissues are still saturating on 21 m they will saturate less on NX50 than on air.
40 sec. ascend time to 15m is without remaining on the 21m depth after the gas change. Call it at least 3:40 min if you remain on the switch depth.
Could you please tell me what is the last SW version before this change in the calculation, because I want to downgrade again. I don‘t see the reason to change my art of diving because you guys decide to change your software.
I think the real issue that this new behaviour is only described in the release notes _somewhere_. We'll try to sum up the OSTC operation for multigas dives so the background to this is more clear. We really try to improve the software and we're using the OSTC by ourself for deep and technical dives as well. When required we roll-back features or make things adjustable. The least we want to do is to force users change their deco strategies. When required we roll back or make certain features optional, of course.
I thank you for your answer. It would be much appreciated if there would be a possibility to force the gas switch at the adjusted depth. The switching depth data are anyway available in the gas adjustments already, so you just have to use them.
as written in the 2nd post, just set the gas in question to type 'Travel' and it will be cued (and put in the calculation) when it is becomming the best gas by change depth and fits into ppO2, regardless of deco constraints.
Downgrading to an older firmware release is strongly advised against, there are so many other fixes and improvements along with the last releases you should not use the OSTC without.
As travel gas it will recommend to switch at 21m, but it won‘t consider the NX50 in the calculation in the Simulator and you have to ajust the ppO to 1.6 also for the travel and bottom gas. Otherwise it won‘t let you switch before 18m.
I think that Matthias his suggestion is much cleaner. In the gas settings you have the switching depth anyway as a value. Just consider it into the code.
the link that quotes (this one, in English) was started by me. You told me that topic had already been raised a few days ago in this one. So I will continue writing in this that I think has more information.
you said ascending to the first stop has been given priority over switching gas.
It is more or less established among technical divers than in dives, with air as botton gas, between 40 and 50 m. the decompressive strategy is made NX50 at 21 m. and O2 at 6 m., with a stop of 2 'minutes at 21 m. once the gas change has been made.
I suppose NX50 and 21m. It has not been established randomly. I think it is related to efficiency, the O2 window, etc. Surely you know much more than me about this subject.
What I do not understand is why the ascending to the first stop (i.e. 15 m.) over switching gas is now given priority.
mobu Wrote:
-------------------------------------------------------
> It is more or less established among technical
> divers than in dives, with air as botton gas,
> between 40 and 50 m. the decompressive strategy is
> made NX50 at 21 m. and O2 at 6 m., .....
In my surroundings technical divers making decodives up to 30m depth use Nx32 as bottom gas and hardly ever choose to carry additional decogas (sometimes O2, but most of the time nothing).
For anything deeper than 30 meters and up to about 60 meters (depending on total deco time) bottom gas will contain Helium (35% or 45%) and only 1 deco gas is necessary (usually EAN50) and is indeed switched at 21m.
Second deco gas is only added on deeper dives or on longer deco's where minimum gas would be a possible problem.
However we don't do deco on Air (we hardly dive Air for any dives actually).
Given that we don't make deco dives on Air and considering small deco (up to 15 minutes) we just do that on back gas whenever gas supply is sufficient and hence we don't add the hassle of carrying additional gases for a decrease in deco time of maybe 3-5 minutes while having a less streamlined configuration and more drag.
Long story short.... I think it's okay to have the software do just as it does now and whenever I decide upfront to switch to EAN50 at 21m I will still make the change and tell the computer I did so. No one should blindly "follow" their computer and in stead should plan their own dive upfront.
I know it. That's the theory and that's the way it should be. But Helium is not always available. Here we say: "Air to inflate bicycle wheels"
It is clear that we can make the gas change through the menu. It's just seems faster with the gas switch suggestion, especially since you have to press the buttons a few times.
And of course, No one should blindly "follow" their computer and in stead should plan their own dive upfront. I completely agree.
The last post is a really good one, because it touches the underlaying question: what is the duty of a dive computer in technical decompression diving?
Propably everyone will agree on that in technical deco diving, one doesn't simply jump in and will take a look on the computer from time to time to see how the deco obligation evolves during the course of the dive. Instead, the dive is pre-planned and its maximums are established: max. depth, max. bottom time and turn press at least. That numbers should be known by the diver, additionally they can be put on a slate for backup-brain.
Now come the options: do i have one or two computers? One computer can fail for various reasons, so a printed run table for the main dive plan along with an independet depth and time gauge is required. Having a plan B table (+ a few minutes and/or meters) in the pocket won't hurt either. In case of two computers, the likelihood of both of them failing completely during the same dive is rather small. Still, if they are same brand and type, what they display can suffer from systematic design or programming failours. In terms of software complexity, depth and time gauging/displaying is rather simple and least likely to be compromised. Calculating a deco schedule is quite complex, and results depend on numerous details like - just for example - the personal gas switching protocol discusses earlier. That is also why very few computers produce identical data even if settings are the same. In the middle of both is the calculation i would call "as of now": current tissue pressures, saturation levels and thus ceiling depth / next stop depth. These data should be in line with the pre-planned dive-table, given the dive was done according to the plan so far. +/- 1 minute doesn't matter here. So here we have the first duty a dive computer can take: check if i am still within my plan as of now.
So what's with the calculated complete deco schedule? Several options: online replication of offline planning results from Multideco and other deco planning software. Hard job. Deco planning tools as of today have lots of options to shape the computations to personal preferences and diving protocols. Most documentations do not disclose how computations are affected in detail by the settings. So 1:1 replication in general isn't possible. Additionally, putting more options into the code makes it more complicated and raises the propability for programming errors.
Another option: replacement of the plan B tables, i.e. calculation of the current "no frills" emergency deco schedule - how to get to the surface within shortest time / gas demand, with the gases still available (-> lost gas function), while staying within Buhlmann + GF limits, fullstop. That's what the OSTC firmware is geared to now. If you have two computers and have reasonable trust in their computations, they could be used to replace the printed tables entirely. Else, or with one computer only, the number of plan B tables could be reduced, using the computer to give emergency schedules for intermediate + time / + depth scenarious, as well as a solution in case of a totally messed-up dive (hopefully never needed).
How to gain trust into the computer's calculations / verify its programming: The build-in deco calculator uses the deco schedule prediction code, thus the most complicated part of the OSTC firmware. The simulator runs in real-time and exactly as during a real dive, just that the depth can be manipulated. Running a planned dive in the simulator in real time thus checks the programming of the "as of now" calculations. As more you rely on the computer in handling your what-if scenarious of your dive, the more you should run them beforehand in the deco calculator and the realtime simulator to gain confidence that they'll work as expected when needed.
So to cut a long story short, the OSTC in its present form is made to back-up a dive, giving ceiling and next stop depth data for "as of now" plus a shortest way home (surface) controlled emergency schedule. When using the gas needs calculation function, it will also prompt when running out of resources for even an controlled emergeny ascent.
I did another deep dive on the weekend, 45 metres for 20 minutes. As I suspected from the first deep dive I did on this new firmware, the computer now operates totally differently to before.
1 Before this firmware update, if you had a deco gas activated, then the indicated deco took into account that you were going to use the nominated gas/gases. If you did not change at the depth nominated, the deco indicated changed within a minute or two, to a higher value based on using the bottom time.
2 If you nominated a deco gas as being active at x metres, as soon as you got to that depth the computer indicated to you that there was a better gas to use.
3 Now, 1 above does not appear to happen.
4 Now, in the case of 2, if you have a gas change set to be (say) 7 metres but the PPO is 6 metres, it will not offer the change till you get to 6 metres.
The above have been confirmed by tests using the planner.
I feel that the above changes are a regressive step. It would be far better to return to how the firmware dealt with gases and deco before this update.
I agree. The computer reminds you at the change depth, when the p02 is suitable. It's an easily understood, simple concept and one that's been taught on tech courses in the past. I much prefer the way the old firmware dealt with this.
Suddenly I am glad to see that there is more interest for this issue. I have wrote my opinion earlier in this posting (on April 1st and it wasn’t a joke) and have opened even a second posting in German.
If I have a multiple gas dive (with one or more NX gases), than I expect that my dive Computer is calculating the dive with the gas switch on the max. allowed ppO2, or at least on the adjusted depth.
Of course I can change the gas whenever I want and the computer will change the Deco plan in a minute, but I want to know it before I jump into the water and not after the gas change. Until now I was using the OSTC for dive planing on the boat between two dives. Now it is not possible any more and I have to use a third party software on my phone to plan my dives.
In the adjustments there is a possibility to adjust the ppO2 for Deco, travel and bottom gases separately. Additionally there is a possibility to adjust the switching depth. At the moment this values are useless. Why don’t you use them and eventually add an auto option? So if the Auto option is on, the computer can calculate the decompression plan on your way. If there is the max. ppO2 for the Deco gas and the switch depth adjusted, please make it calculate with those values.
Earlier in this posting (or maybe it was in the German one) you have wrote, that the gas change on the way I do it (and as I could read in the last two posts before mine, I am obviously not the only old fashioned one) is not actual any more. Well, I had the chance to talk to several instructors from different organisations in the last few days. They still teach the people on the same “old fashioned” way, so everyone (or the most of the people) are diving like trained.
Personally I like my OSTC, but in my opinion this change was a step into the wrong direction.
I think I understood what you wrote, although I do not see the direct relation that it has with the subject beginning of the topic "gas change suggestion".I think everything you've written previously is compatible with the previous function "gas change suggestion".
I totally agree, the dive is pre-planned and you should dive that plan. We have all learned this mantra. It is clear.
How do we pre-planned a dive? With a deco tool, like multideco, v-planner, etc. Obviously, I will try to configure my OSTC parametres to match the plan chosen in the deco tool. Also, I can use the deco calculator functions built into the OSTC or OSTC planner v3.00 beta 14 and put on a slate for backup-brain.
So now, I have a computer with a complete deco Schedule, and the same plan and plan B table (+ a few minutes and/or meters) in the pocket.
If my computer fails, and I'm diving as planned previously, I will continue with the deco schedule written in my wetnotes and my independet depth and time gauge.And I know, that the schelude deco will be the same one that my computer would show me if it were working.
If I understood you correctly, what you propose is to replace replace the printed tables entirely. So, you need two computers. And I understand that, if possible, of the same brand and model.
I do not understand what in case of a single computer. You talk about using the computer to give emergency schedules for intermediate + time / + depth scenarious, as well as a solution in case of a totally messed-up dive. So, you're supposed to dive according to the pre-planned and use the computer for emergency scheludes. I'm sorry, I think this part I just did not understand.
Do I understand correctly if I say that the ostc in its present functions is equivalent to deco on the fly or decoratio?
my last post was an excursion into some thinking on what will be the responsible job of a dive computer in technical diving, to deduce why it (the OSTC) does the calculates the way it does them. Was an attempt to bring some reasoning based on deco theory into the discussion.
It has nothing to do with deco on th fly: the OSTC doesn't interpolate anything, it recalculates the deco every couple of seconds. By doing so, if you want, it can free you from carrying a multitude of backup-plans with you for every +1 minute and/or +1 meter step. Instead, you could leave these plans to be computed on the real dive profile to the OSTC and just carry one backup-of-the-backup plan for the worst scenario to which you switch when running out of plan A and additionally the computer fails.
but want to understand how it works at it seems the the gas change hint come to late?