There are an estimated 9 million recreational scuba divers in the United States(Taylor, <http://www.wemjournal.org/wmsonline/?request=get-document&issn=1080-6032&volume=014&issue=02&page=0083#i1080-6032-014-02-0083-b2>). The average recreational dive is between 15' and 130'. When diving, one experiences a change of pressure as one descends and ascends. The change of pressure is 14.7 psi/33' freshwater and 14.7 psi/30' salt water. The difference in the change of pressure is due to the added weight of the salt content in salt water.