POLAR M21 - Manual (Page 49)

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8. For a small percentage of people the heart rate
variability will not totally disappear with increasing
workload. In this case the age-predicted limits are the
best estimation for the exercising zone.
...THE OWNZONE LIMITS BASED ON HEART RATE
VARIABILITY (OZ.V) VARY CONSIDERABLY?
Heart rate variability reacts sensitively to all changes taking
place in the body and environment. The OZ.V heart rate
limits are affected by, amongst others, your daily state of
fitness, the time of OwnZone determination, the type of
exercise and state of mind. The lower limit of the OZ.V
heart rate limits can change for the same person by as
much as 30 beats.
However it is important that the feeling of exercise carried
out in the OwnZone is light or moderate. For example if
you raise your heart rate too rapidly after the first stage,
you may get too high OwnZone heart rate limits. If the
OwnZone limits seem to be too high we recommend that
the OwnZone determination is done again.
... SOME OTHER PERSON USES MY POLAR M21 OR
POLAR M22 HEART RATE MONITOR?
Polar Heart Rate Monitor determines the OwnZone heart
rate limits on the basis of heart rate and age. If someone
else uses your Polar M21 or Polar M22 it is necessary to zero
the OZ.L heart rate limits which are in the memory. Reset
the age in the USER mode.
Even though the user is the same age as you the age must
still be reset in order that the OZ.L heart rate limits are
zeroed. If this is not done the Polar M21 or Polar M22 may
give the following user OwnZone heart rate limits based on
your heart rate variability which is stored in the memory of
the equipment.
Note that changing the user also affects the calculation of
the total calorie expenditure (Tot. KCAL) and cumulative
exercise time (Tot. TIME). If these readings are not zeroed
when the user changes, the Polar M21 or Polar M22 adds
new exercise periods into its memory, even thought the
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