Looking for some other info, I came across the following quote in section 12.2 of the
MPS User Manual:
For accurate flow measurement, the zero flow value must be calibrated regularly,
therefore “Automatic calibration of zero flow” is activated by default. If activated,
the sensor will perform a calibration of the zero flow value when the pump is not
running, for example if the PC is in standby and the sensor is still powered by USB
connection. If you decide not to use automatic calibration, you will have to manually
perform a calibration on a regular basis by clicking “Set current flow to zero”
when the pump is not running.
Which I read to say 'have a permanent USB connection to the Flow Sensor'.