I don't think Fresenius TSC requires a calibration of the transducers.
The machine automatically carries out a plausibility check of all 4 before its starts the A02/P02 test.
We stopped doing calibration as a routine part of the PPM about 18 months ago. I think we now get through far fewer transducers, no apparent increase in related failures.
I haven't done a service for >12 months so I may have this wrong.