Sensorless Flow Measurement with ACS880

In its manual, ABB ACS 880 drives can measure flow accross the pump without any sensor.

What is the configuration for this at ACS880 drive?
Which parameters should I set?
If a Manual states it can measure flow as suggested, then I would expect it to state the principle of operation and what parameters are set to achieve it.

The nearest I could imagine is when the drive is connected to a positive displacement water pump where generally flow is directly proportionate to motor speed. However it is not entirely linear and some parameters would be guesswork, so would only be a guide to flow without any accuracy.