Mine was a certified Floscan 201. The info with it said something about calibration being necessary to cope with installation variables. The unit was 10 – 12% out initially but has been consistently accurate (2% ish) on Mogas for several years now I have calibrated it. It was time-consuming getting it absolutely right.
Professionally, we fitted over 800 of the things with remote links back to base. The data was compared with ECU info, fuel added etc etc for predictive health monitoring and fuel planning (non aviation application). All the units required calibrating, but were fine for some considerable time after.
Rod1