it all goes 'orribly quiet when you run out
Folklore.
When I run a tank dry in my bugsmasher, the engine stays noisy. The prop still runs at whatever RPM it was set before the motion lotion ran out.
All measuring systems are subject to error, or more correctly, order of accuracy. Light aircraft fuel contents gauges are notoriously inaccurate and unreliable, flowmeter systems not much better, until you get into heavy iron, and there it is still around +/- 3% order of accuracy.
Rubbish.
The digital flowmeter in my bugsmasher is calibrated to +/- 1 litre in 300. Either that, or all the fuel bowser flowmeters at all the aerodromes around Australia are as precisely inaccurate as the one in my bugsmasher.