Unless you weren't breathing for part of the dive , yes you can use the average depth from the computer. It is the easiest way to work out Avg Depth for a complete dive unless of course you are using a deco gas when things become a little more complicated to work out your bottom gas SAC.I have a quick question on this topic:
When calculating your OC SAC after a "normal" incident free dive, is it correct/accurate to use your average depth for the entire dive (as shown on a computer) for the depth part of the calculation? (i.e. if my Suunto tells me the average depth for a dive was 20m, can I calculate my SAC by working out my air consumption in litres per minute and diving this by 3)?
Is this too simplistic?
hmm I don't think your SAC rate should decide any size of twinset, it is far easier/simpler to use the same size set as you buddy - this make gas planning much more straightforward.
But working out your SAC should be done over a few dives so you can come up with an average litres per min.
A better way of translating sac rate into something useable underwater is to come up with a number of bar per 5 minutes, this helps significantly in working out how long your gas supply is going to last.
So lets take an example. I am going to dive to 10m using a 10l cylinder, and my normal SAC rate is 20LPM.
10m is 2ata so I will be using 40LPM each minute for 5 mins. this is 200l of gas divided by cylinder size equals 20bar.
So I will use 20bar every 5 minutes at 10 metres, so if I have 150bar of useable gas it should last 37.5 minutes.
The same maths apply to any depth or any size cylinder, you just need to have a good handle or your SAC rate over a variety of conditions.