Which technology is that sensor using?
What Horner claims could be true, we all know fluid flow meters in racing were in fact never very repetitive, not even for integration, let alone instantaneous readings. Everyone that I know uses the "calculated" fuel flow (linear with the accumulated injection time, mostly) in pro racing (WRC, F3, motoGP...) and the error is not greater than 1% over long periods of time, as long as injectors and fuel pressure are ok.
I also thought from day 1 this is a huge mistake in the regulations. I do not imagine the end of the story, apart from duplicating or triplicating the sensor and assuming the random part of it as part of the game. Still a terrible system, though.