What is the difference between gauge pressure and atmospheric pressure and how are they different from absolute pressure
Gauge pressure is the pressure acting on the unit area(zero references is current atmospheric pressure at the place of installation).
Atmospheric pressure is the pressure of air molecules in surroundings acting on a unit area. Absolute pressure is the pressure acting on the unit area ( zero references is an absolute vacuum)
Gauge pressure = absolute pressure - atmosphere pressure
Absolute pressure= gauge pressure + atmosphere pressure
Atmosphere pressure = pressure of air molecules in ambient acting on a unit area.