If an absolute pressure gauge reads 56.5 psia and atmospheric pressure is 14.7 psi, what is the gauge pressure psig reading?

To determine the gauge pressure from an absolute pressure reading, you subtract the atmospheric pressure from the absolute pressure. In this case, the absolute pressure gauge reads 56.5 psia, and the atmospheric pressure is given as 14.7 psi.

To find the gauge pressure (psig), the calculation would be:

Gauge Pressure (psig) = Absolute Pressure (psia) - Atmospheric Pressure (psi)
Gauge Pressure (psig) = 56.5 psia - 14.7 psi
Gauge Pressure (psig) = 41.8 psig

This method of calculation makes it clear that the gauge pressure reflects the pressure over and above atmospheric conditions. Therefore, the gauge pressure reading calculated as 41.8 psig correctly represents the difference between the absolute pressure and atmospheric pressure.