Gauge pressure is the difference between the absolute pressure and the atmospheric pressure. It is the pressure that is measured by a pressure gauge.

$$ P_g = P - P_{atm} $$

Where:

- \(P_g\) is the gauge pressure in Pascals (Pa)

- \(P\) is the absolute pressure in Pascals (Pa)

- \(P_{atm}\) is the atmospheric pressure in Pascals (Pa)

2. Absolute pressure

Absolute pressure is the pressure measured relative to a perfect vacuum. It is the sum of the gauge pressure and the atmospheric pressure.

$$ P = P_g + P_{atm} $$

Where:

- \(P\) is the absolute pressure in Pascals (Pa)

- \(P_g\) is the gauge pressure in Pascals (Pa)

- \(P_{atm}\) is the atmospheric pressure in Pascals (Pa)