J.P. Instruments EDM 960 Twin Pilots Guide - Manual (Page 33)

For Your Safe Flight Page 28
Section 6 - Fuel Flow Operation
Fuel Management
Without a means of measuring accurate fuel flow, you must rely on the
aircraft fuel gauges or total time of flight. Aircraft fuel gauges are
notoriously inaccurate (they are only required by the FAA to read
accurately when displaying empty). Determining fuel consumption by
multiplying time of flight by estimated flow rate is, at best, an
approximation, and assumes a constant fuel flow rate for each phase of
flight. However, the EDM Fuel Flow Option uses a small, turbine
transducer that measures the fuel flowing into the 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 flows into the engine. Prior to engine start you inform the
EDM Fuel Flow Option of the known quantity of fuel onboard, it
subsequently tracks all fuel delivered to the engine.
IMPORTANT !
For EDM fuel calculations to be accurate, it is
mandatory that you inform the EDM of the correct
amount of usable fuel onboard the aircraft and confirm
proper operation of the fuel flow transducer prior to and
during flight. Do not rely on fuel flow instruments to
determine fuel levels in tanks. Refer to original fuel flow
instrumentation for primary fuel management
information.