Step 1:
Connect the pressure switch to a pressure source e.g air supply via a hand pressure regulator and test gauge, as shown in the diagram above.

Step 2:
Use an Ohmmeter or a Digital Multimeter (DMM) set to the continuity range to check and verify that the switch contacts are as indicated: NO (Normally open) and NC (Normally close).

Step 3: 
Connect the Ohmmeter or DMM between the normally open contacts(NO) and the common terminal (C) of the switch. The meter should read "open circuit". Adjust the hand pressure regulator to increase the pressure to the setpoint of the pressure switch until the contacts change over. The meter should now read "short circuit". Note the pressure reading and write it down. This pressure is the switch setpoint for a "rising" pressure.

Step 4:
Increase the pressure to the switch to its maximum rating. Slowly reduce the pressure to the switch until the switch changes over from closed to normally open again. Note and write down this pressure reading. This pressure is the switch setting for a "falling" pressure.

Step 5:
From the readings you have taken work out the pressure difference between the rising and falling pressure settings. This is called the "dead-band" of the switch. The dead-band calculated should be equal to or less than the manufacturers’ dead-band.

The maximum dead-band is usually stated by the manufacturer. The switch is unserviceable if the maximum dead-band is more than the manufacturer's recommendation (dead-band on the nameplate of the switch)

To calibrate the switch for a low pressure, go through the steps in this order:
Step 1 to Step 2 to Step 4 to Step 3 to Step 5