Acumen Stopwatch Instruction Manual page 46

Select Target Zone (TZ) Mode (Optional)
Freezes for two seconds
From the Analog Time Display, press MODE/NXT Button two times to
D
enter the Select TZ Mode. There are three Heart Rate Target Zones in the
watch. In this mode, you can select Heart Rate Training Zone, Set Target Zone
Limit, Out of Target Zone alarm, and Heart Rate Sampling Interval Time.
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