# Gauge Pressure

```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.
```

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