So you haven't even done a 2 hour dive and you're arguing about the "best" way to (somehow) do 2x 3hr dives? You sure have a lot to say about dives you're not actually doing. And you claimed I would be crazy for doing 6hrs on 6lbs of sorb already, but now you're admitting its not nuts at all.
For the record, I did 6x 3+ hour dives and 1x 2hr dive last week with
@girlwithbigtanks. An entire week's worth of diving longer than your lifetime longest. Neither of us were diving Revo's... Sorb was about $3.50/lb in MX, we probably "wasted" 8lbs worth in the week, $28 of the cost of our $2000 cave diving trip (~%1).
I admitted that it's feasible when you specify really warm water.
Your second paragraph is back to the "sorb is cheap" argument.
@stuartv voting logic failure is not one-ish time, ask some of the guys that were around in the 90's and early 2000's, it's killed at least half a dozen that I can recall.
Revo is still sold with dreams, but the dreams have no bearing on my comment, it is still 100% applicable to a unit with a Shearwater controller and Shearwater monitor.
If the Revo is sold with a solenoid, it is intended by the manufacturer to be run from that solenoid, not manually.
Here's an example that I hope helps you see where this is coming from. Also this is applicable to real engineering world, not just rebreathers and is the reason that you don't see 5-engine airplanes.
Revo.
If one cell on each side fails,
you will have useless deco information from the NERD because it averages the 2 readings, and you will still have a fully functioning controller side.
If 2-cells on the controller fail, you will have accurate deco information from the NERD but a malfunctioning solenoid controller and inaccurate deco information on the controller.
You also have to pay attention to 2 different sets of information coming from 2 different locations and go back and forth to see which one you agree with after a dil-flush.
[snip]
Liberty-
Any 2 cells fail, you tell it to ignore those 2 cells and you retain full function of the rebreather AND accurate deco information from both handsets. Can be 1 cell on each side or both cells on one side, doesn't matter in the slightest. All 4 are showed together on either the handsets, HUD, or now ODA.
Please explain how situation 1 is better? CMF's are NOT parachutes no matter what your instructor or the manufacturer has told you. They can NOT maintain a ppO2, only slow down the decay. If you are running the unit in parachute mode, which I do most of the time, then the parachute still works. If you are running the unit from the solenoid which I do when doing working dives, then it still works.
Now, what is important is that we are talking strictly about the number of cells in the system and their configuration factoring into reliability of a system. We are not talking about how those systems talk to each other and the failure modes inherent to that type of configuration because the initial argument was that 5-cells doesn't cost more than 3 because you aren't replacing them any more often which is rather hysterical in and of itself given the regular premature failure of cells, but also how 5 cells is vastly better than 3. I would argue if it was, then the rest of the world would have adopted it by now. The issue with the arguments about your brain being the final say is that
@Shearwater still won't give us the ability to manually disable cells like Divesoft has. If they did that and put haptics in the handset I would gladly switch back and dive their computers on my rebreather, but until then I have had cells start doing weird stuff underwater and the ability to manually disable them instead of rely on voting logic is the biggest safety improvement in my diving.
Best system for me is 3-cells where I can manually disable them when they go on the fritz which is what I have on my primary rebreather. One goes janky and the display tells me it's doing weird stuff and is voted out. I dil-flush and confirm which ones are weird and disable them. That's the ticket!
That is incorrect. If the NERD is running 2 cells and they diverge by more than 20%, then the NERD will calculate deco based on the lower ppO2. If they are within 20% of each other, then I don't see a problem with the deco calc being based on the average. If not, then you potentially get overly conservative, but safe, deco calcs. So, not correct to say that the NERD would give you "useless deco info".
However, in that scenario, the controller is working fine, so no problem.
Paying attention to 2 sources of information is the all day, every day way we dive CCRs. If one goes out to lunch, then we turn the dive and rely on just 1 of those sources. What's the problem?
Also, isn't your own CCR substantially different in config than how the manufacturer builds and ships them? So, you're now diving a "non-functional" CCR (or whatever terminology you want to use), but you're trying to make it sound like diving a rEvo in manual mode is somehow a problem? "If you ordered the optional solenoid, then it is not intended to dive in manual mode." That sounds awfully dogmatic.
So, you're saying that in the 90s and early 2000s, several people died as a result of having 2 cells go bad at the same time and voting logic pushing them hyperoxic? Has that ever happened to anyone on a rEvo? Has it happened to anyone at all in the last 10 years?
Not sure where the "CMFs are not parachutes" comment came from. I never said they were. I DID say that having the CMF makes flying it manually easier. I don't have to inject O2 manually as often, when flying manually. For that matter, my solenoid doesn't fire as often (as it would with no CMF), either. I never said or implied that it was a parachute.
You think it's hysterical that someone would say the 5-cell unit doesn't cost more for sensors. And you cite regular premature failure of sensors as a reason. Can you point me at any examples of people using rEvo cells that are having regular premature failures? I mean, I know I don't have much experience myself. My almost-3 years with mine and no sensor failures at all (except for the 2 I soaked in caustic and replaced) is just an anecdote.
Personally, I would not (and did not) say a rEvo costs no more than other units for sensors. But, I will say that the difference in annual cost is negligible to an overall CCR diving budget. To me, anyway.
I totally agree with you that I would like to be able to disable individual sensors in my Shearwaters. It would be nice to know that I could have 4 cells go bad and still end my dive and get out with one of my computers doing deco calcs based on real-time, observed data.
But, the reality is that not having that ability is such a small deal that I would not pick a different electronics package because of it. I have 5 cells and I could have any 3 of them crap out and still fly the unit manually to get out, still with safe deco calcs. Worst case, I would have a longer-than-needed deco because the NERD is calculating it based on a falsely low O2 sensor value. If any 2 sensors go out, I don't even have that downside. And if the one low sensor is the bad one and it's unacceptably low, I can always change the NERD on the fly to calc on internal SP and continue to fly manually.
If your scenarios, comparing the Liberty with 4 and the rEvo with 5, yes, I would prefer the rEvo, every time. If 2 on the rEvo go out, then if 1 or both are on the NERD, no issue at all. If both are on the controller, I fly manually. Probability of that: EXTREMELY LOW.
The rEvo does not have a redundant solenoid or CMF. It doesn't have redundant manual adds of anything, either. But, it does have completely redundant monitoring of ppO2 and redundant deco calculations (when properly optioned).
Knocking it for having 5 sensors is just silly. It's better than having 3 or less. It may not be better than 4, when you have the ability to disable individual sensors. But, I can't see that it is worse than 4. I would be inclined to say 5 with Shearwater and 4 with Divesoft seem pretty equal.
But, like the ability de-water the rEvo, I think knocking it for having 5 sensors is 1000% overblown baloney that really boils down to "it costs more to get started because you have to buy 5, instead of 3." So you may spend a little more each year on sensors. Compared to all the rest of the money you spend to dive and dive with a CCR, that extra sensor or two is total noise in the budget. Knocking rEvo for that is even sillier than knocking it for not being able to de-water it. You got enough water in it to have to bail? Okay, you brought enough BO, so that's not an issue, right? Just like any other CCR that may have who knows what issue that forces you to bail. If the rEvo were inclined to flood on a regular basis, that might be a reason to knock it. But, if it's an extreme rarity to flood (which I think it is), and the flooding is merely an inconvenience when it happens, then how big of a deal is it, REALLY? If having to bail is more than an inconvenience for you, then you might need to have a talk with your instructor - because ANY CCR can have an issue that forces you to bail. That's why we carry bail out.
When you are diving a unit that you can dive without carrying bail out, then I'll knock the rEvo myself!
You will learn how to be more aware 
