Quick question from a newb about air integrated computers

[fnfalman]

Mechanical relays are more prone to failure than solid state. But there are no mechanical relays in an SPG. Analog pressure gauges have existed for a 100 years (actually more). They are generally pretty bombproof.

Except for the inherent accuracy. Analog SPG can have error reading up to 150-PSI or even more. That means if you have a reading of 500-PSI, you may only have 350 or even 250. My fancy OMS SPG is about 125-PSI off. The pressure gauge on the tank gauge checker is about 200-PSI off. Both of my computers (different manufacturers) are within 25-PSI of each other.

 

[Phil_C]

As a new diver (recently CMAS qualified) I thought long and hard when I bought my first and second stages about AI or analog SPG or both. I'm fortunate enough that cost wasn't a limiting consideration, rather how did I want to dive. During training I had only used analog guages until my last couple of dives prior to qualification when I was lent a dive computer.

I went for a wrist mounted AI dive computer with a compact triple console analog setup (depth/pressure and compass) as a backup. On each of my first four dives after qualification I checked the analog SPG against the AI and the AI was conservative - i.e it was showing (slightly) less than the analog gauge. Since then I have just clipped the triple console up out of the way and not bothered with it. I am happy with the AI, and have confidence in it, but have a backup should I need it.

I am not risk averse (or I wouldn't be taking up diving) but it makes sense to me that in the event of a computer/AI failure I have a backup so I can ascend slowly watching my depth and use up my remaining air in surfacing in a controlled fashion which gives me the best possible off gassing option etc. without having to rely on my buddy too much. This is pretty much what I was taught to do in the event of a computer failure and seems to hold true/safe for this situation.