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We were taught 1 finger per 100 psi. We still use that. No ambiguity. A quick flash is always 5 fingers, the last flash is held for several seconds to allow proper comprehension. You only need to actually see the last signal. Flash Flash Flash 3 fingers is 1800. I can be happy with any system that uses only 1 hand and minimal brain power....
The best I've see recently, in Bonaire, was a request to make a T (like a timeout signal) for a half tank, and a fist for a low tank, namely 700 psi or 50 bar....
Well "end the dive" does not work very well if you are a 15 minute swim away from the fringin boat...I found/find hand signals to indicate air pressure confusing and mostly stupid. No standardization and I'm not likely to remember some strange system that I've not used before. In fact I'm not very likely to remember any system. I keep very close track of my air. I expect you to do the same. All you need to signal me is "end dive".
The half tank T system sucks...It is very inadequate. Not granular enough.
Agreed. This was the first time I have been on a dive where the DM only wanted to know about half tank and nothing else. Nada. The DM made an assumption about his divers without talking to us...Maybe he was used to Noob air hogs?For PSI, maybe. We use it to indicate 100 bar since we pretty much only dive Al80s, so starting out at 200-220, max. Fist for fifty and/ fingers for 10 works fine from there, and is more than granular enough.
I don't think I've ever been on a guided dive where the half tank was all that was asked, but 'requiring' people to signal it gives a quick impression of air consumption in a group at a point where there's still plenty of gas in everyone's bottle.