Computing your SAC
(Surface Air Consumption)

You can compute roughly how much gas you'll need for a particular dive if you track your past consumption.  The rate a diver consumes air while diving is known as SAC.

As a diver descends, the gas breathed becomes denser.  Air is delivered from the tank at the depth's ambient pressure.  This means that at 66fsw, in the time it would take to breath 1 cubic foot of air at the surface, you will have consumed 3 cubic feet or air at this depth. 66fsw = 3 atmospheres.

The following script can help you determine a diver's SAC rate.
WARNING!  UNDER NO CIRCUMSTANCES IS THIS CALCULATOR TO BE
USED A DIVE PLANNER OR ESTIMATOR!  SEEK A PROFESSIONAL'S
ADVICE BEFORE ATTEMPTING TO USE OR INTERPRET THIS DATA.