Can the IN191 Blood Flow Meter be calibrated to measure absolute values (flow) in a perfusion chamber?

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. 

Although it might work to calibrate the Blood Flow Meter, the probes have not been tested for linearity.
For absolute flow measurement, a Transonic ultrasound Flow Meter should be used. It has the advantage of factory calibrated probes for different media, temperatures and flow rates.