[Stephan Whelan]

When I first saw this question I thought to myself...

"Gee...good question, I suppose i'm going to have to hunt down some expert to answer this question for our visitors!"

And once again I have been proved that the sheer quality of people browsing the forums and answering questions is of the uttermost level.

Thanks for the comprehensive answer Eric - you've proved your skill is beyond just being a top level Freediver!