Suunto Cobra question

[St.jimmy]

Hi! Me and my dad bought suunto cobra, and while his is shipped, I got some pool time with mine. When I read it first (after bleeding the tank to clean the valve, and purging and breathing from the second stage to check the air), it read 2985 PSI (3000psi AL80), Perfectly reasonable. However, once in the water, the gauge read 3007 psi, counting down one psi per second, eventually settling at 2900-and-something psi, 39min airtime, 12 feet (new,nervous diver, esp. last night) . So, what happened? Was it just "catching up" in dive mode?

[fireflock]

was the pool water warmer than the air?

[St.jimmy]

A little bit, why? Air expansion, maybe?

[CompuDude]

Air expands when it gets warm. Fill a tank in a cold room, leave it in the sun for an hour, and it will measure higher pressure.

Usually the reverse happens... hot fill a tank, take it while it's still hot, jump into 52 degree water, and watch your SPG drop 200-300 psi without taking a single breath.

[BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)]

Yep, the water warmed the air which increased the pressure.

[St.jimmy]

Two Questions;
One, Why so much? It was only a couple degrees difference.
Two, Why did it count down so fast and then stabilize?

[rox@ucf11]

39 min at 12 feet wtf.... id be down there for like 1:30 hrs am i missing something i know that wasnt what u were askin but...

[St.jimmy]

We were late getting there-we were getting pool practice before our make-up o/w dives-and the DMs were about to leave.

[BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)]

The pressure differences do not seem that great. The regulator system is dynamic. Probably just everything settling in to a steady state.

I don't even look at the 1s and 10s digits and I think the fact that they are there gives a false sense of accuracy. In effect I treat the digital pressure gauge just like it's an analog SPG.

Even if the reading really is accurate to the nearest PSI, in what way does it benfit me to know that I have 2327psi versus 2300psi?

[kroorda]

Speak english.