Citizen E610 Instruction Manual page 102

[Calculation of fuel consumption]
Q : If the fuel consumption rate of an aircraft is 250 gallons/hour, how many gallons
of fuel are needed to fly 6 hours ?
A : Align 25 of the outer scale with the "  " of SPEED INDEX of the inner scale.
Result: 1,500 gallons - 15 corresponds to 6:00.
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