It was a special treat to watch NASA astronaut Scott Parazynski (the only person to reach both outer space and the top of Mount Everest) learn the delayed feedback of ballast trimming to try to hit a target depth without overshooting.
He drew many analogies to his five trips to the space station and seven spacewalks. He replaced the CO2 scrubbers, which bore a visual similarity to Apollo 13. I had to request that they carry duct tape on every dive. =)
He told us that when their CO2 levels hit 3%, they had to end their spacewalks. We kept it well below that, but had to surface when we found a wreck on sonar but the CO2 crept to 1% with all of our heavy breathing.
He starts off tall, too tall to fly on Soyuz as he learned the hard way after learning Russian and preparing for the flight only to be disqualified the end of the process!
But on the ISS, he elongates by a full 2.5 inches as his spinal disks expand in microgravity. This came back to haunt him on his first Everest attempt, where high on the mountain, his L2/L3 disc ruptured, requiring surgical repair. He was ever the optimist. Up there, he said, there is an unlimited supply of ice for your back.
Driving the sub
The four thrusters operate much like the 
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