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Gauge Pressure Objectives • Describe gauge pressure. • Correctly calculate the gauge pressure for a given depth of either fresh or salt water. • Apply the concept of gauge pressure to scuba. Main Points • Gauge pressure • Calculating gauge pressure • Application to scuba Description • Uses atmospheric pressure as zero. Example 1 Calculate gauge pressure at 57' of fresh water. Answer: (.432psi/ft) x 57' = 24.6 psig Convert the answer above to absolute pressure. Answer: 24.6psi + 14.7psi = 39.3psia Example 2 Calculate gauge pressure at 57' of salt water. Answer: (.445psi/ft) x 57' = 25.365 psig Convert the answer above to absolute pressure. Answer: 25.365psi + 14.7psi = 40.065psia Application to Scuba • The concept of gauge pressure explains why an analog depth gauge will not give an accurate reading of depth when diving at altitude. • Care to explain? – An analog depth gauge uses 14.7 psi as 0 ft – at altitude you must dive to some depth before you reach a pressure of 14.7 psi Main Points • Gauge pressure • Calculating gauge pressure • Application to scuba Objectives • Describe gauge pressure. • Correctly calculate the gauge pressure for a given depth of either fresh or salt water. • Apply the concept of gauge pressure to scuba.