why analog?

[Cheekymonkey]

When you say combining two functions amascuba you mean a computer htat does depth, time and gas?

 

[amascuba]

Combining functions as in combining normal depth/time (as all computers do) with spg functions.

 

[diver12345]

Spg's are cheap $56 bucks online compared to 550 or so for a cobra. It is bigger and bulky whick gets in the way of the stage bottles. Not to much with one but try it with two or three. I had a cobra in my first diving days. It has given me false info on 2 occasions. Both times false depth readings of 30ft and 20ft deeper than I actually was. If the computer fails then you loose depth,preasure,and time.A spg fails all you loose is preasure.

 

[TomP]

Let me preface this by saying I have no tech experience, but I am now acquiring my gear and diving with it before getting into technical diving.

My question is this: I just bought a Suunto vyper, and already have a cobra. Would the cobra be a good substitute for an analog SPG?
......

thanks

Before we get to the Cobra, if you just bought the Vyper you might consider exchanging it for a multi-gas computer. The incremental cost isn't high and when you get to accelerated deco you can leverage those capabilities. Otherwise, you'll have to put iyour Vyper into gauge mode and then all you have is a really expensive bottom timer.

About the Cobra. My view, you already have it so why not continue to use it? If the size becomes an issue you can trade it out for an analog and bottom timer.
Personally I prefer analog SPG and think there is some merit to point that for AI a single failure takes out two functions but since its your backup timer and you'd be thumbing the dive anyway I don't see it as a big deal.

The claims that electronic devices are less reliable seems pretty much like reflex left over from when there was little evidence one way or another. Also, I think the notion that if a solution is not better, it is somehow worse, is flawed; there should be room for equivalence.

 

[Scared Silly]

I have had three pressure transducers fail on computers. Not one analog SPG. One read 4800 psi, two others read low. That said I like having AI. But for any trip I carry backup guages incase something goes tits up. Also depending on the enviroment I can switch remove the AI and dive with a spg.

There is also the issue of AI with a the use of the evil transmitter. Lots of discussion on this.

Mechanical Precision:
Analog is about +/- 0.5% whereas digital is +/- 0.25% on a 0-5000psi range.

Mechanical Accuracy:
If calibrated properly both have the same accuracy - i.e truth. Both can be just as screwed up.

Arithmetic Accuracy:
Analog has a resolution of 50psi (i.e. there are marks for every 100psi) Digital down to 1 psi.

Putting it all together, both have the same number of significant digits. For instance, the analog is +/- 25psi but you can only read down to 50psi so if your gauge reads 1150psi you really do not know if is 1175psi or 1125psi or in between thus only the first two digits are significant and the last two do not mean squat. The same for a digial gauge, +/-12.5psi so even if it reads 1142psi you do not know whether it is 1164 or 1130 or in between. So the last two digits are not significant either. So either case you have 1100+psi.


NOTE: you can compensate for mechanical accuracy but not mechanical precision.

 

[Cheekymonkey]

I could be wrong Scared Silly, but I would imagine that the mechanical precision is dependent on the specific brand and parts you are talking about.

 

[Atticus]

One of my regular dive partners likes using a digital SPG (I don't recall the brand). His SPG will display the pressure whenever there is pressure present. I have lost 3 dives now due to him opening a valve the night before to check the pressure in his doubles, and forgetting to bleed the line to turn the SPG off, the batteries draining, and him no longer having a working SPG. He usually discovers this after we've suited up and are ready to jump in the water.

An analog SPG doesn't share this failure mode. Some computer SPG's don't share this failure mode.

Why not use a normal small analog SPG? What advantage are you looking for by using the computer? You won't want to unclip every time you do a depth/time check, so you can't use it as a primary bottom timer in any case.

 

[Scared Silly]

I could be wrong Scared Silly, but I would imagine that the mechanical precision is dependent on the specific brand and parts you are talking about.

Brand does matter quality does ... Many gauges are made by the same company but then rebranded. Pelagic makes most of the compases. Oceanic made a lot of Sherwood's gauges at one time.

 

[TomP]

....
Why not use a normal small analog SPG? What advantage are you looking for by using the computer? You won't want to unclip every time you do a depth/time check, so you can't use it as a primary bottom timer in any case.

Based on the original post, the advantages would be that he already owns it and thst it could serve not only as his SPG but also as a fully redundant computer that uses the same algorithm as his primary.

 

[Cheekymonkey]

Yea already owning it should be a big factor