Paul Braunbehrens writes:
> Mark, I'm pretty opinionated, but here goes (since you asked
> for opinions).
> A computer needs to do a few things to qualify, in my book.
> 1) user replaceable battery

IMO, it really depends on how long the battery lasts and therein lies a
Catch-22: when you design for a User-replaceable battery, its easy to
undersize the battery so that it only lasts a few days/weeks/months and gain
a smaller size that's more convenient to wear on one's wrist or whatever.

However, in general, I don't mind sending a dive computer in to the
manufacturer every 3-5 years for a $75 battery, as opposed to needing to
open the thing up (and subjecting it to Murphy's Law) 2-4 times per year for
a $15 "User" battery.  Not only can the former be potentially less expensive
(particularly if you fail to reseat the O-ring properly and cause a flood!),
but it has at least been my experience with my current computer (with an old
Monitor I) that when the computer is returned to the factory for a new
battery that they'll double-check its  calibration, etc, which is also
clearly worth something.

> 2) activate automatically upon water entry


> 3) nitrox capability

I'll probably go for this feature as well.  I'll also look for the ability
to set the mix, as opposed to it being limited to just Nitrox I & II.

> The suunto vyper does these 3 very well, and it will also function in
> gauge mode, allow you do download your dives to your PC, and it uses
> a pretty good model (Reduced Gradient Bubble).   I think it's about
> $300.

I was looking at the Vyper within the past year or so and while it really
looks promising, I didn't care for the fact that it had a very definite
"safety stop" that was pragmatically mandatory.  I was on holiday last week
and got in some diving and due to surface conditions on one dive, I pulled
my primary stop at ~25fsw.  I don't recall technically if this would have
been permitted or not within the Vyper's model, but I know that it would
have been close to being disallowed, or perhaps more accurately "not

> Suunto also makes an integrated one, the cobra.  It's basically a
> vyper with air integration.  I'd stay away from it.  Buy a nice
> gauge, and you don't need it.  The only real failure mode in gauges
> is that they stick (if they are old and mistreated).  This is an easy
> failure to spot.  If the gauge hasn't moved when you look at it
> again, then it's sticking.

Agreed.  The main feature of Air-Integrated (AI) dive computers tends to be
the strong suction that they put on your wallet.

Mark writes:
> >
> > What functionality and features are lost with the  AERIS
> > 300G when compared to the other two fully integrated computers?
> > It is quasi-A/I, in that the analog SPG does couple with the
> > computer(to some extent), but I am not sure exactly what
> > features are lost versus the fully integrated systems.

"Quasi-AI"?  Do you mean that it is a hosed-AI system instead of the newer
(and more things to go wrong) "hoseless" AI types?

If the computer is using the tank pressure in any fashion, there needs to be
an A/D conversion device, which generally means a piezoelectric transducer.
If there's a traditional analog gage in the console, this probably means
that there's simply a "T" HP fitting hidden inside the console that supplies
the HP air to both devices.

Generically speaking, the thing you're gaining with any AI computer is an
air consumption based "time remaining" prediction.  But since the
assumptions that go into that value are invariably very simple/primitive
(constant depth, SAC, etc), the information provided is often bordering on
useless trivia.  This is particularly the case as your air consumption
improves to the point that your bottom time is "deco limited" instead of
being "air limited".

> > OTOH, I have a degree of concern about relying on a single
> > integrated digital SPG.  Over the years I have occasionally
> > experienced computer malfunctions, but have never had a
> >  problem with an analog SPG.

Generally speaking, I like the old, traditional analog SPG.  There's very
few things that can go wrong with it and its failure modes are pretty
intuitively obvious in their nature.

When it comes to electronics and saltwater, literally anything can happen.
I've had more than enough electronic strobes & watches go flaky and the one
thing that they all have in common was that they were all quite
unpredictable in their failure modes.  They were all essentially sudden
failures - when the saltwater electrolyte hit their circuits, some were
silent, others screaming.  None of them have any sort of pseudo-failsafe
"limp home" mode.

FWIW, so long as you have something hanging off of an HP hose, if the gage
dies, with some practice, you can still estimate by hand to some degree your
remaining air supply simply by feeling the rigidity of your HP hose.