As with all new divers I found that I was using air at a very high rate, with the consequence that I needed to end the dive while my buddy still had plenty of air remaining.

I decided to graph my air consumption rate, using the following formula to calculate my equivalent surface air consumption (SAC)

To give a worked example, assume the following:

Litres used = 2160

Dive time = 45 minutes

Average depth, (from computer) = 20 metres

SAC = 2160 / 45/(20 / 10 + 1)  = 16 Litres per minute

The chart shows maximum depths of each dive, and the equivalent SAC.

As the graph shows my consumption dropped dramatically during the first year, to the extent that I am no longer the one to call the dive because of lack of air. This data stopped at the end of 2005 as I then switched to a rebreather.