How long does a tank of air last

[Kim]

These days I get a SAC readout from my computer. The way I was originally taught to do it was to decend to 10 meters (33ft) write down the Bar reading on my slate, swim around maintaining the 10 meters depth for a period of time - 10 minutes/20 minutes, it doesn't really matter - write down the Bar reading at the end of the timed period. It is then simple to work out your SAC rate. You can do this swimming slowly, or swimming hard. Obviously the SAC rates will differ, but it gives a fairly real idea of the air you will use in different conditions.

 

[Rafael]

Being very new to this and a bit wet behind the ears.

Will be nice to have more information, but i will give you some idea from my last dive

I dove an average of 12mts. for 56 minutes using 1450 psi the water temp was 7 C.

But is so many factors is hard answer, but i will say if you are doing a shallow dive in a temp over 15C i will say an houer.

 

[Blackwood]

In theory yes, but remember that the way you breathe and react sitting at the surface in a lawn chair may be vastly different than how you normally breathe while finning (or even hovering) over a reef.

Indeed. I'm just giving a suggestion for those without the equipment (digital bottom timer/computer) to compute a quasi-accurate average depth.

And 10 minutes is probably more necessary to see much significant change (in the way of data) on your spg.

Absolutely right. The change over 1 minute on the surface would likely not even be legible on an analog gauge.