First Dive Computer

[scubadada]

-- R.W. Hamilton et al, The DSAT Recreational Dive Planner, Development and validation of no-stop decompression procedures for recreational diving, 1994 Feb 28, pp. 7, section II.C. 3.



-- Ibid, pp. 14. section III.B.3. (emphasis mine)

There's a whole section II.C.6 titled "Safe or reliable; DCS is not an accident" in there, too... I think the difference in our diving styles is I've actually read this stuff and I (usually mostly) comprehend what I read.

Is there a point here relevant to the discussion?

 

[scrane]

Your BSAC bias keeps shining through. Remember that this is a thread on 1st computer purchase by a newly certified diver. As before, you keep confusing the main issue by injecting deco diving into the mix. Please try to stay on topic.

Diving with a Suunto is like driving a car in a 40 mph zone that has a speedometer that only goes up to 35.

 

[dmaziuk]

Diving with a Suunto is like driving a car in a 40 mph zone that has a speedometer that only goes up to 35.

... and there's never a SCUBA cop with a Doppler radar when you want one.

 

[Jay]

Did you read e.g. the DSAT paper? The discussion of underlying assumptions, design goals, the interpretation, parts about confidence intervals etc.? If so, read the ScoobyLoo rubbish and see if you spot the difference.

Pressurizing a bunch of computers and looking at their reading at a few random points proves only one thing: that they had those numbers at those points in the process. Nothing less, nothing more. And as I ecall they couldn't even get the same numbers the second time around.

The 126 page 1994 DSAT RDP document has it's goal clearly stated. Scubalab's article also has its goal clearly stated. (wrt NDLs and taking the computers together on a dive). These two goals are different.

all available evidence suggests that on the 1st dive with no additional conservatism, all algorithms should be within 2 minutes of each other at the most

Scubalab's data shows that for their Dive 1 in 2014, 2016 and 2017 your statement is wrong.

(I don't have 2015 report / data - unsure if they did it).

 

[Jay]

All the computers could do all the dives. So it doesn’t matter which computer a diver used in that test.

They used a metric ‘NDL’ which is mathematically very sensitive. Very small changes in input result in large changes in the metric. So the EXACT dive profile is greatly magnified. Likely as not going a couple of m shallower a little earlier on a ‘conservative’ computer would increase the NDL by a large percentage.

If you want to know how conservative or aggressive a computer is really then do a deco dive and see how long the stops are. Long stops mean a lower surfacing oversaturation and less risk, so more conservative.

Thanks for that interesting point. I wonder, would running a series (and a variety of dive profiles) of Scubalab style tests (and not taking the computers into deco) be a valid method to compare conservatism for a Rec (only) diver (who typically wouldn't got into deco (as defined by a deco stop, exc a SS))?

 

[doctormike]

It's funny how these arguments always come down to algorithms, when for a recreational diver that's probably the least important feature. Every single modern dive computer that you can buy will reduce the chance of a recreational diver getting bent to extremely low percentages. And the bottom time difference usually isn't so great (I guess people have different opinions about that!).

Things that are far more important to me are bulletproof reliability, readability, a user replaceable and widely available battery, and amazing customer support. Guess which company hits all of those marks with flying colors...?

Now I DON'T recommend Shearwater for people getting started who aren't prepared to spend that much on a DC. You can get a fine DC for far less than that, but I think that all of those other features are worth the cost differential if you can pay it. Maybe not what the OP was looking for, but something to consider for other divers reading this thread. And they are still terrific computers for people who will NEVER do tech diving as well.

You get what you pay for. If this was a car forum, and someone said that they recommended a BMW, I doubt people would say that it's a ridiculous suggestion because a Kia will do exactly the same thing (get you from place to place), or say that they were just for racers. I'm just saying, those Canadians seem to be on to something good...

 

[KenGordon]

Your BSAC bias keeps shining through. Remember that this is a thread on 1st computer purchase by a newly certified diver. As before, you keep confusing the main issue by injecting deco diving into the mix. Please try to stay on topic.

If we are going to be arguing about where to draw absolute lines about safe vs unsafe noticing that really there is no such line (NDL is not that line) and there is just increasing probability of being hurt. So NDL is when that probability gets ‘too high’. To keep the probability lower you can either do shorter dives or stops (ignoring other common factors like hydration, surface intervals, seesawing etc). These are the facts of going diving. They are not confusing the issue, they are the issue. If, as asserted earlier, one computer says doing a 57 minute dives requires stops and another one does not then that new diver ought to understand what that means. You seem to want them to believe it is because the manufacturers are mean spoilsports, not because they would be safer doing the stops.

 

[KenGordon]

Thanks for that interesting point. I wonder, would running a series (and a variety of dive profiles) of Scubalab style tests (and not taking the computers into deco) be a valid method to compare conservatism for a Rec (only) diver (who typically wouldn't got into deco (as defined by a deco stop, exc a SS))?

Yes, but you’d need to dive the computers to the actual limits. That is practically quite awkward and these sorts of magazines turn out to have very limited staff resources

At the end you might be able to say brand X gave Y minutes more bottom time than brand Z though the day when diving such and such cylinders. Knowing what happens if you dive brand X to brand Z’s limits would be interesting though. If the answer is that the mandatory brand X stops are shorter than the brand Z safety stop then the dive profile could be identical.

 

[KenGordon]

It's funny how these arguments always come down to algorithms, when for a recreational diver that's probably the least important feature. Every single modern dive computer that you can buy will reduce the chance of a recreational diver getting bent to extremely low percentages. And the bottom time difference usually isn't so great (I guess people have different opinions about that!).
..

It usually kicks off when someone repeats the Scubaboard Lore that Suunto are rubbish because of RGBM following someone saying not to worry about the algorithm because it will not often be the limiting factor. Then DSAT fans with air consumption to boast about claim they are the limiting factor and follow up with assertions that staying down longer is just as safe as not staying down longer.

 

[KenGordon]

You get what you pay for. If this was a car forum, and someone said that they recommended a BMW, I doubt people would say that it's a ridiculous suggestion because a Kia will do exactly the same thing (get you from place to place), or say that they were just for racers. I'm just saying, those Canadians seem to be on to something good...

A Shearwater is not like a BWM. I own both. A nice car is really much nicer than a nasty car, or even an average utilitarian car. My Perdix is not much better than my Helo2. The screen is nicer (but not as nice as an Eon) but the two button interface sucks in comparison to the four button one. Imagine a web browser with no back button... However, most of all the computer is a very small part of diving enjoyment, whereas the car is actually pretty important in driving enjoyment. Of course if you can’t afford the fuel a BMW isn’t as much fun as a Kia. Choices have to depend on circumstances too.