Deciding on gear--SPG + AI computer or computer only?

[Peter Guy]

To safely do a dive you need to know three pieces of information -- time, depth and pressure. The Vyper Air, when it works, which is almost all the time, will give you those three pieces of information, no problem. BUT, and here is the "but" when it doesn't work, it is most likely because it has either failed to sync or has lost sync and then you lose your pressure (or as an instructor friend of mine likes to say, the amount of time you have left to live). It is highly unlikely that the Vyper Air will suddenly stop providing you with time, depth and NDL information (if the latter is even relevant).

Given the likely fail mode, a simple SPG that you can clip off on your left side makes sense to me.

IF you then want to have a backup for the rest of the information, get a 2nd computer or a bottom timer. (For example, I just saw a Zoop being offered on ScubaBoard for $150 and it would be a great backup for you since the NDL algorthym is the same as for your Vyper.) Especially if you are planning on taking your gear on diving vacations/trips, having the backups just makes sense.

For what it's worth -- I use a Vytec AI wrist mount and have a Cobra clipped off as my backup (actually primary) SPG. It also serves as a redundant depth and time guage -- and then I have a Zen too which is something my old eyes can actually read!

 

[scubadada]

My goals are to preserve the current dive I'm doing, subsequent dives that day, and subsequent dives in the sames series. I dive an Oceanic, air integrated VT3 as my primary along with a Geo2 and SPG as backup. Both run the DSAT algorithm and are perfectly matched. I've had no problems to date. I've had the VT3 since 7/10, 250 dives and the Geo2 only since 9/11, 140 dives. If I do have a failure, I am reasonably confident I will be able to dive without interuption. I consider 2 failures in the same series of dives to be extremely unlikely.