Citizen 520 Instruction Manual page 10

[Chronograph Timing]
1. Start timing by pressing button (B).
* The chronograph is repeatedly started and stopped by pressing button (B).
2. Pressing button (A) resets the chronograph to 0 seconds.
Time
Stop
Reset
(B)
(B)
Measurement
(A)
(A)
[Note]
The chronograph continues to keep time with the chronograph hands until it is
stopped even after 60 minutes have elapsed. Once timing is finished, promptly
press button (B) to stop the chronograph, and then press button (A) to reset it
to 0 seconds. If timing is allowed to continue, the battery will continue to wear
down and eventually be depleted causing the watch to stop before the end of the
indicated battery life.
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