A head count would seem the preferred method. I would be interested in Wookie's input on this subject...
Wookie's input on the subject:
Head counts are completely inadequate and only a new captain would consider performing one. Roll calls are little better. When I do what we call a "welfare check", every diver meets the eye of the captain. If someone is in the head, in their bunk, making out on the bow, whatever, they will have to meet my eye and tell me that they are OK. This gives me an opportunity to look deeply into their eyes and see if they have a nervous twitch, like might result from a type II hit. It also gives me the opportunity to hear in their own words how they feel. Of course, it also means I have laid my eye on every stinky diver on the boat, and the boat may now move.
You'd be surprised at how many folks regard this as an invasion of their privacy. They get upset that I interrupted their nap, dinner, makeout session, etc. They are offended that I didn't take their word for it that their wife, brother, sister, whatever is OK, and that I want to see everyone's smiling (or other) butt on this boat before I let the deck crew off the deck.
I am one of the very few captains that has left someone at sea forever. We never found them, their body, or any evidence of their passing. I knew, however, before all the divers were up that he was missing. He should have been the first one on the boat as he had been every other dive. Before half of the divers were up from that dive I was calling the other boats, then the Coast Guard. My system works for me, not for everyone, but it works well here. I hate the shorter trips because the captain doesn't have time to learn the divers names. It is critical that the captain come down from the flybridge and conduct the roll call where he can see every diver, and not have to worry about missing one because 2 divers yell "here" when the name "Mark" is called.