Citizen E610 Instruction Manual page 103

[Calculation of the flight time]
Q : If an aircraft consumes 220 gallons per hour, how many hours can it fly when
consuming 550 gallons fuel ?
A : Align 22 of the outer scale with the "  " of SPEED INDEX of the inner scale.
Result: Two hours and thirty minutes - 2:30 corresponds to 55 of the outer scale.
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