As an empirical device, each size of Parshall flume has had to individually calibrated to obtain the discharge equation.  For smaller flumes, these calibrations took place in fluid mechanics labs. 

The typical process is:

• The flume is installed in a long, straight channel. 
• The flow rate is regulated by varying the number of pumps on the feed line and by means of a valve located on the line.  In some instances, a NIST traceable magnetic flow meter is place inline.
• The flow enters the flume’s channel is allowed (or forced) to assume a normal velocity profile before it enters the flume.
• In a stilling well, a hook / point gauge is used to measure and record the water level at the various points of measurement in the flume.
• After passing through the flume it is discharged into weigh tanks where the water is weighted over a given time period to obtain the flow rate.
• The water is then discharged from the weigh tanks into a recirculation sump.