How much does alg matter for rec dives? Cheapest buhlman DC?

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@KenGordon, deepblu seems to be able to make a much nicer screen at an affordable price. As I read your post it is obvious that you know know way more about diving than I ever will. It Just seems like someone else should be able to build something that looks like it was designed in the 21st century at an affordable price. My 13 year old who is just finishing up his certification, laughs when we go into the lds and look at computers. While I wait for that to happen I will have to settle for a mares puck pro, Aries A300, or bite the bullet and pick up 2 deepblus.

This is not about know about diving but about how to make stuff.

The Deepblu computer uses a segmented display. That ought to be much less power hungry than a proper colour display. Basically you get something like a traditional Suunto or the controller for your boiler but in multiple colours. Presumably though that is less flexible than a bunch of pixels so they have opted to setup via a smart phone. Now they need a radio and so the power budget is spent there. The backlight for the display probably costs a lot too. So they end up with a rechargeable battery.

The killer is that you go to buy 1k screens and have to wait until someone else wants the other 99k and then six months later when you want another couple of k you find they don't make them anymore. The Deepblu approach avoids that by having a bespoke design. The people that serve that market expect smaller volumes and a need to keep design stable. The conventional pixel based displays used in higher end dive computers probably come from suppliers to mobile phone manufacturers and have different expectations of volume etc.

I have never seen a Deepblu computer and know nobody who has so I cannot comment on how it turns out as a package.

With dive kit the expectation and reality are often quite different. If you think you need feature X which nobody else seems to care about or is not served by mainstream manufacturers you might want to spend extra effort testing your assumption. If possible try stuff out before buying. Ask people you know what they use, ask them why and if your concern is an issue for them. It is a diving cliche "you don't know what you don't know", it applies to kit as well as training.
 
I have a few cheap crap xxFire 18650s that I use in a flashlight when biking home from work late. They're 2-2.5 years old and some of them don't hold enough charge for 2 15-minute trips anymore. With proper quality control etc. Suunto may get ones that are much better, but Li-ion lifetime was still ~600 charging cycles last I checked: dis/charge it every day and it'll last 2 years, dis/charge it every week and it'll last over a decade.
Your charging cycles number is not to total death but to some XX percent drop in capacity. Part of the game in care and feeding of these batteries is how fast you charge and discharge them. Gentle use leads to longer life, that means that bigger batteries are triply better, they provide more capacity when new, need fewer cycles and die more slowly for a given number of cycles.

In practice this means that an undersized battery is a really poor design choice.
 
@KenGordon, deepblu seems to be able to make a much nicer screen at an affordable price.

The problem is that they have a nice-looking screen and a low price, but they missed out on the third important part: Battery life. They don't last very long at all on a charge. People charge their smartphone every day, but don't want to have to charge a dive computer every day. You can charge your phone while you're using it, if you forget to charge it the night before....

On top of that, the way they lock you into creating an online account and only using their app and Cloud to update settings on the Cosmiq and download your dive data reeks of plans for datamining for profit. And I don't want my data being used for profit by anyone. Especially not in exchange for a cheaper computer. Or maybe it's just a plan to make money from advertising that you are forced to see when you access their website where your dive data is stored. Either way, I don't like it. And if that was NOT their plan, they could have saved themselves HEAPS of money by just working with the Subsurface developers (or Diving Log or any other 3rd party dive log developer) to get support for the Cosmiq added and then directing users to use Subsurface (or whatever) for their dive logging.

I could be wrong. Maybe their business model is based very simply on increased sales by having all these social media features built in. But in that case, my personal opinion (which is worth what you're paying for it) is that they would have even more sales by not spending all that money on Cloud app development and just selling the Cosmiq for an even lower price. Especially if they also ditched the smartphone apps (supporting iOS AND Android is an expensive pain in the butt) and just built it into the dive computer to manage all the settings. Investing in smartphone apps and a Cloud infrastructure is all expensive and needless - unless those things are going to pay for themselves somehow...
 
The whole screen quality is my big gripe as well. Why can I get a 55" 4k tv for $400 (I know it is not the greatest quality) but have to settle for a dive computer screen that looks like a gameboy screen from the early 90's? When is the dive computer technology going to catch up the tv's and smart phones?

Battery life is still the biggest problem. Look at even people like Apple who have massive distribution - their apple watch battery only lasts about a day.
 
Right now I think I've narrowed my list down to 2 DCs:

1. Aeris A300 - because it's like the VEO 2.0 and is only $200. The $90 cable is the killer for me right now, though.

2. The upcoming Deep6 computer. ($140+$20 cable). I don't really like their screen layout, even in dive mode, but it seems to be one of the better value options out there that runs Buhlman. If you need a cable, this is nearly 1/2 the price of the Veo+Cable above, and even cheaper than the Veo + cable once the Aeris is completely discontinued.

I could probably get away with the Suunto Zoop for a similar price ($140-150 new on ebay + a $10 generic cable), but I don't like that they run RBGM. (Mind you, it probably doesn't really matter to me because I'm doing rec diving only).

There's no word from Deep6 on the new release date, but I'm guessing it would be closer to Q3/Q4 this year based on all their latest changes.
 
The problem is that they have a nice-looking screen and a low price, but they missed out on the third important part: Battery life. They don't last very long at all on a charge. People charge their smartphone every day, but don't want to have to charge a dive computer every day. You can charge your phone while you're using it, if you forget to charge it the night before....

On top of that, the way they lock you into creating an online account and only using their app and Cloud to update settings on the Cosmiq and download your dive data reeks of plans for datamining for profit. And I don't want my data being used for profit by anyone. Especially not in exchange for a cheaper computer. Or maybe it's just a plan to make money from advertising that you are forced to see when you access their website where your dive data is stored. Either way, I don't like it. And if that was NOT their plan, they could have saved themselves HEAPS of money by just working with the Subsurface developers (or Diving Log or any other 3rd party dive log developer) to get support for the Cosmiq added and then directing users to use Subsurface (or whatever) for their dive logging.

I could be wrong. Maybe their business model is based very simply on increased sales by having all these social media features built in. But in that case, my personal opinion (which is worth what you're paying for it) is that they would have even more sales by not spending all that money on Cloud app development and just selling the Cosmiq for an even lower price. Especially if they also ditched the smartphone apps (supporting iOS AND Android is an expensive pain in the butt) and just built it into the dive computer to manage all the settings. Investing in smartphone apps and a Cloud infrastructure is all expensive and needless - unless those things are going to pay for themselves somehow...

The Deepblu Cosmic runs a very conservative, proprietary version of Buhlmann ZH-L16 as the decompression algorithm. Even on the progressive, most liberal setting, it is very conservative. This is another variable that may be taken into account by some divers.
 
1. Aeris A300 - because it's like the VEO 2.0 and is only $200. The $90 cable is the killer for me right now, though.

Everything except Mares Pucks comes with ~100 cables. Cosmic is the only entry-level one with BT.
 
I hear over and over that Suunto's RGBM is some proprietary undocumented algorithm. But it's really not. There are multiple papers (and a book) that describe exactly what the algorithm does. It is not a bubble model by the way, and it doesn't generate deep stops (unless you enable the deep "Pyle" safety stops). The particular version known as "Suunto RGBM", "Mares RGBM" etc. is a normal M-value based model, except that it uses three functions to reduce the permissible M-values for repetitive and reverse profile diving consistent with the "real" RGBM model.

http://www.scuba-doc.com/rgbm.pdf is one of the papers that contains the formulas (see the "RGBM/ZHL (Critical Parameter) SYNTHESIS" chapter, page 16 and following). The formulas are the f_rp, f_dp and f_dy defined on page 18.

This is the part that a lot of people criticize as being too conservative. In reality, if you understand how these functions behave, you can work around it. The key is to avoid repetitive dives within a certain surface interval window. Either do the next dive very quickly (though you might still have too much tissue saturation in that case), or have a good hour of surface interval before you go on the next one. There are plots of this function (f_rp) available on the Internet, or you can do it yourself in WolframAlpha. You will see that there's a time window where this variant of the RGBM will be very conservative for repetitive dives, but once you're outside that window it's really not too bad.
Also keep in mind that these functions are not just made up to make the computer more conservative. They are supposedly based on actual measurements (though I haven't checked the data myself), in combination with the (full) RGBM model. Now the model might be wrong, and the conservatism is really unnecessary, but I think it's more likely that there is at least some truth to this particular prediction of the model, in which case you will really want the conservatism (we're not talking about deco diving here, so these predictions are pretty separate from what was tested in the NEDU deep stop study which questioned certain other predictions of the RGBM). Diving a more liberal computer doesn't actually make your dives safer! It only hides the actual risk.


In addition to this, Suunto RGBM also adds mandatory safety stops when violating the 33ft/min ascent rate. That particular part is not openly documented (as far as I know), but it's not doing anything crazy in my experience as long as you have your ascent speed under control (unless something goes very wrong, your "mandatory" safety stop will never be longer than the regular 3 minute safety stop).

Now the Suunto EON is a different beast. It is one of the very very few computers available today that implement the actual RGBM bubble model (Suunto calls it Fused RGBM). The EON does not use the formulas that I talked about above. In recreational diving, it will behave in the same way, but if you go into deep or decompression diving, it will behave more similar to a VPM-B computer and generate "real" deepstops. Now publications for the "real" RGBM are a mess. The basics of the model are available, but - as someone who has recently tried to implement it myself - the details are often missing. I do believe Wienke when he says that the model has been checked against their dive databases, but if you do very deep or aggressive decompression diving, I wouldn't be surprised if the model or its implementation had some significant flaws.

In the end, for recreational diving, I think the algorithm doesn't really matter all that much. I personally think that the RGBM assumptions about bubble seeds across repetitive dives are plausible, and I would rather go with a computer that opts to be more conservative here. But I'm not sure if there's much support from actual empirical data on this, so I wouldn't want to make any claims that this is the one correct choice. In the end I tend to agree that for recreational use, the form factor, clarity of the display, reliability/quality and ease of use are are probably more important than the algorithm.

Edit: Found a plot of the reduction functions: They are on page 8 of this PDF by Suunto: http://ns.suunto.com/pdf/Suunto_Dive_Fused_RGBM_brochure_EN.pdf
Actually the one hour of surface interval that I mentioned is still a bit short, but that's roughly the point at which the additional conservatism of this algorithm starts decreasing again. After two hours, everything should be close to a regular non-RGBM computer again.
 
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If I am in the market for a rec computer now I would only consider anything under US$200.00 eg. Mares Puck Pro or Sunnto Zoop. But if I have the time then I would wait for Deep 6($139.00).

Down load cable should be FOC but some manufacturers do like to rip you off!!!!!!
 
https://www.shearwater.com/products/swift/

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