Martel Electronics DPC300A - Manual (Page 21)

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5. Apply pressure with the pump slowly until the switch opens.
Note: In the switch test mode the display update rate is
increased to help capture changing pressure inputs. Even
with this enhanced sample rate the device under test
should be charged slowly with pressure in order to ensure
accurate readings.
6. Once the switch is open, "OPEN" will be displayed; bleed the
pump slowly until the pressure switch closes.
7. In the top display it will now read "SW OPENED AT" and give you
the pressure at which the switch opened.
8. Select the "NEXT" option to display the pressure at which the
switch closed and the hysteresis.