(Jerry Parker - 18 days ago)I was a young NAUI dive instructor in the early '70's . SDM classified ad for DB O2 Rebreather caught my eye. I modified the unit by fabricating a canister for the same media we used in anesthesia. Added "aquamaster" mouthpiece and hoses. As I recall the total unit was chest mounted with the O2 cylinder and flush valve (Rt.) low about belt level. In those days we captured reef fish and combed the Santa Fe River in FL for fossils. I had read all of Hans Hass's books and in anesthesia (CRNA) we knew all about closed systems so this was easy and fun. Did experiment with depths to 55' but only short exposures with no ill effects. Great article!