I was diving last week in Roatan and our average dives were to 60 feet with a dive time of 50 minutes and I would end up with 700 to 800 PSI left, however if I didn't take my camera with me I would have 3 to 4 hundred lbs more. Taking pictures would not seem like a lot of tasking but obviously it is.
Bruce
YMMV. Others have reported that bringing a camera along improves their SAC, since with a camera in hand they tended to slow down and look more closely at the small things around them.
My observations on SAC are:
1. If you are working hard, then you need to breathe a lot to clear out the CO2. The secret to having low SAC is avoid working hard.
2. If diving is hard work, then you are most likely doing something wrong.
The most likely candidates are:
1) You aren't neutral and are going around negatively buoyant while continuously finning upward to maintain depth.
2) You are not horizontal. Moving through the water is much easier if you are horizontal.
3) You are inefficient. Using your hands to propel yourself or adjust depth is inefficient (you have those big monster fins on your feet for a reason). Your finning technique may be lacking.
4) You are going too fast. If you slow down, your SAC will come down. Long ago I found that that, outside of things like coral, sea stars, and sea cucumbers, pretty much everything down there can easily outrun me.
3. My personal experience is that cardiovascular fitness does not affect my resting SAC, but improved fitness greatly reduces how fast my SAC rises as I work harder. In other words, fitness level doesn't affect my SAC for slowly puttering around the reef, but good fitness level helps reduce my SAC when doing a long swim at 1 knot. (This is my personal observation only. There doesn't seem to be a general consensus on this)
4. Your SAC at any given point in your dive history is what it is. Plan your dives for what your SAC
is rather than what you
wish it would be. Don't be any more embarrassed about your SAC than you are about your height. It is what it is.
5. Step one is to reduce your workload. Only after that does it make sense to pay much attention to breathing. For me, I find what works best is very long inhale/exhale cycles, with a large portion of the cycle spent with lungs near full. Personal observation. Sample size of 1.
6. SAC follows a typical learning curve cycle --- rank newbies have very high SAC which rapidly falls as they learn to be able to get neutral so that they can stop finning and stay where they are. After than, the SAC reductions come more slowly with such things as improved finning techniques.
In general, you don't lower SAC. You change how you dive and that affects your SAC. SAC is not a goal unto itself.