The PWP Scanning modality measures the beat-to-beat variation in heart rate. This natural rise and fall of heart rate is caused by autonomic nervous system activity.
PWP shows us how well your body can or cannot adjust to stress in the environment.
Studies have shown that a reduced PWP is associated with poor long term health, while an increased PWP is associated with good long term health.

In the diagram the white square should score somewhere in the green box, the further away (in any direction) from the box the worse the score.