Divers who giant-stride into cold or less-than-pristine water environments will surely appreciate this perfectly matched first and second stage pairing. The MK17 is a high performance, balanced diaphragm first stage engineered specifically for cold water and harsh environments. Completely sealed off from the elements, neither water nor pollution can get inside the chrome-plated marine grade brass body to foul the inner mechanism. This total sealing system also allows for a dry ambient pressure chamber which works to prevent freezing, provides better protection and improves performance, assuring you of trouble-free operation no matter how cold or murky the water gets. The MK17 is also user-friendly, offering two high pressure and four low pressure ports, two of which are high-flow (high-flow ports deliver about 15 percent more air than conventional low pressure ports). In addition, it comes with an external intermediate pressure adjustment that allows technicians to maintain peak performance between service intervals without having to break down the first stage. The A700 second stage, with its metal casing, screw-down casing cover, metal valve housing and over-molded accents, exhibits a real muscularity in design. Its air-balanced valve technology and oversized exhaust valve work in conjunction with a well designed sectional exhaust tee, a first-rate purge and responsive user controls -- including a diver-adjustable micrometric inhalation effort knob -- to create a rugged, reliable breather with effortless inhalation and an ease of exhalation that is unmatched. The MK17/A700 was built for demanding divers and demanding conditions. With every breath you can be guaranteed top-of-the-line performance, no matter what kind of water you're jumping into.