J.P. Instruments EDM 700/800/711 Pilots Guide - Manual (Page 32)

Page 28 Engine Data Management
To reset to zero the amount of fuel used at any point in time, manually
step to display
USD and hold both buttons for five seconds until the
display shows . 0 USD.
Fuel Management
Without a means of measuring 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). And measuring time of flight is only an
approximation, and assumes a constant fuel flow rate for each phase of
flight.
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 aboard, and it will keep track of all
fuel delivered to the engine.
Parameter Scan—Systems with Fuel Flow Option
Listed below is the sequence, parameter description and example of the
digital display. The first column indicates what position the select switch
must be in to display that particular parameter. T is EGT, F is FF and A
is ALL.