WEBTEC HPM110 Operating Instructions Manual page 17

Caution!
The zero point correction sets the current ACT value to
zero. In order exclude erroneous measurements, ensure
no system pressure is being applied when carrying out
this function.
This initiates the zero point correction. The ACT (actual)
value is indicated in the display as 0.0 bar. The
correction remains active until the device is turned off.
OFL/ZEro is
seconds if the measured pressure
(0 bar) is greater than 5% of the
measurement range.
Zero point correction cannot be
carried out. Please ensure that no
system pressure is being applied.
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