Calibration with a commercially made flow meter:

In the image above we have the commercial flow meter on the left, a m/s to km/h conversion in the centre and the open flow meter on the right.

At first the open flow meter was providing a reading 4 times faster than the reading from the commercial unit, but after adjusting some settings both units give quite similar readings. Additional work needs to be done, however so far this will be more than good enough for GCSE, A Level and IB students usage.