J.P. Instruments EDM 760 Pilots Guide - Manual (Page 35)

inaccurate (they are only required by the FAA to read accurately when
displaying empty). And measuring time of flight is only an approximation,
and assumes a constant fuel flow rate for each phase of flight.
The EDM-760 Fuel Flow Option uses a small turbine transducer that
measures the fuel flowing into each engine. Higher fuel flow causes the
transducer turbine to rotate faster which generates a faster pulse rate.
Because the transducer turbine generates thousands of pulses per gallon of
fuel, it can measure with high resolution the amount of fuel that the engine
has consumed. Prior to engine start you inform the EDM-760 Fuel Flow
Option of the known quantity of fuel aboard, and it will keep track of all
fuel consumed.
For Your Safe Flight Page 31