Timex Intelligent Quartz Manual page 235

Clearing the countdown timer value: If desired, you
may clear the value of the countdown timer to zero.
This can only be done if the countdown timer is not in
operation and has been reset. If the countdown timer is
running, you must first stop the countdown sequence
by pressing button A, followed by pressing button B. This
will stop and reset the countdown timer to the currently
selected time value. To clear the countdown timer value
to zero, push and hold button B for two seconds. You
should now follow the instructions to set the countdown
timer value to the new desired length of time.
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