The INL191 Blood Flowmeter is primarily designed to measure microvascular blood perfusion and records only relative changes in an arbitrary unit of BPU. There is no way to obtain any 'absolute' reading/value like [mm/sec] from the INL191 Blood Flow Meter.
For absolute flow measurement, a Transonic ultrasound Flow Meter should be used. It has the advantage of factory calibrated sensors for different media, temperatures and flow rates.
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.