The chronometer is for short periods of time (for example, time before a procedure turn), and does not count more than an hour. You turn that on with the round knob in the bottom-left side of the instrument.
For total elapsed flight time, including hours, you must use the arrow-like knob in the bottom right side of the instrument, which must be in “run” position. With that you can time your 9 hour trans-atlantic flight.
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