Hi Eoin, in the Environment Agency we used to send them to Switzerland (METAS) to run through the tow tank ever 3 years to check performance. This facility is due to close very soon and we have been working with Sontek UK to find a solution. they now have a tank that matches the one used in San Diego for initial instrument calibration setup. they can run the Flow trackers through the same test at 1 or 2 speeds (think its 17cm/s to check the instrument is still performing as expected. we have told all our area teams to carry out a 3 yearly performance test by sending the instrument to this tank based in the UK. Lee Pimble or Rob Thompson are the europe sales guys who can sort you out a quote if you want to go that route.
Olly