When you took dive lessons you learned to perform specific skills to make you safe and comfortable underwater and at the surface. One of those skills was buoyancy control. Once you start diving for fun you use your buoyancy control devise constantly throughout the dive. Your Octopus or Alternate Air Source devise on the other hand is never used unless there is an Emergency Out of Air Situation. Reacting properly in an Out of Air Situation can make the difference between an eventful dive and a tragedy. If your alternate air source and your BCD inflator devise are one and the same you will always know where to find it in an emergency. The Air XS 2 is two devises in one - an extra second stage and a power inflator. Since it's at the end of your BCD inflator hose, it's always easy to find. Using the Air XS 2 is simple. Pressing the oblong blue button inflates your BC; pressing the round blue purge button expels water from the extra second stage so you can breathe from it. To inflate ate or deflate the BCD manually, use the button at the very end of the unit. Weighing 7.9 ounces, the Air Xs has a compact yet sturdy housing less than four inches in diameter. It can be used with nitrox mixtures up to 40 percent.