You can read the pressure guage if it is placed directly against the mask and is luminous. Place a light on the guage and then after charging it then hold the guage directly to the glass. A compass, a small bubble type can be sliconed INSIDE the mask. You have to have good eyes to read that close, when I was young I could of course, now, not.
Yes, I have dove in absolute zero visibility many times, mostly various rivers in Louisiana to recover this and that, outboard motors, sunken boats, lost fishing gear etc. Not only zero viz but currents, swirling currents, barge/boat traffic, and often quite deep, got run over by a tug pushing a chemical barge, I was 40 or more feet down and it sucked me off the bottom and spit me up behind the tug--this despite my stabbing my SeaHawk into the bottom to anchor me. Lights generally are of no use in such conditions other than it is comforting being able to see the glow of a powerful dive lamp from two inches away--lol. I always used a J valve, always checked constantly that it was still up in case I could not read my spg, watch or depth guage. No big deal. Made a few bucks which was OK for a college kid on a budget, solo of course so I did not have to split my cash.
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Yes, I have dove in absolute zero visibility many times, mostly various rivers in Louisiana to recover this and that, outboard motors, sunken boats, lost fishing gear etc. Not only zero viz but currents, swirling currents, barge/boat traffic, and often quite deep, got run over by a tug pushing a chemical barge, I was 40 or more feet down and it sucked me off the bottom and spit me up behind the tug--this despite my stabbing my SeaHawk into the bottom to anchor me. Lights generally are of no use in such conditions other than it is comforting being able to see the glow of a powerful dive lamp from two inches away--lol. I always used a J valve, always checked constantly that it was still up in case I could not read my spg, watch or depth guage. No big deal. Made a few bucks which was OK for a college kid on a budget, solo of course so I did not have to split my cash.
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