HeartMath emWave Owner's Manual page 41

If you're in a stressful state, your HRV wave may not move as high and
low (up and down) on the Heart Action Strip. It will hover more around
the center indicating a lower range of HRV. Breathe more deeply if this
happens and use the Quick Coherence technique. In the Advanced
Mode you have two goals: to increase your coherence and get your
HRV wave to move higher and lower.
The figure on the next page shows the four HRV ranges on the Heart
Action Strip. emWave automatically changes its display to indicate your
HRV range. It is the number of lights on the top and bottom of the Heart
Action Strip that indicate the range of your HRV pattern. If your range is
low (5 BPM) then you will see 4 blue lights at the top and bottom of the
Heart Action Strip.
If your HRV range is high (20 BPM) then you would see only one light
at the top and bottom of the Heart Action Strip. The moving blue lights
in the middle of the Heart Action Strip traces your HRV pattern; rising
as your heart rate increases and falling as it decreases. These displays
give you a better indication of your HRV range.
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