The invention relates to a device, a system for the device and a set of methods used to extract pulse wave features and select an optimal combination of these features for calculating and determining the level of fatigue and fatigue related indicators of a subject. The device and its methods is meant to be used primarily for personal health care diagnosis and home use but can also be used by therapists, trainers and physicians to help them diagnose their patients and follow their patient's progress. The system is designed as a means of accurately obtaining, measuring, registering and interpreting the pulse to determine the level of energy or level of fatigue of a subject. By collecting pulse wave features, selecting those that are most significant and developing algorithms, the device and its method calculates the user's levels of fatigue and fatigue related indicators or personal energy.
