Power output, speed and air comsumption of pneumatic tools are measured with an air pressure of 90 psi at the tool with the tool operating.  Static pressure is the pressure measured in an air line when no air is flowing, and is always greater than the pressure measured under conditions of air flow.

The amount of restriction in the air lines and the volume of air being used determines the difference in static pressure readings and those reading taken with air flowing.  The difference in these reading is known as the pressure drop.