Abstract: 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 blood glucose level and discriminating between different sources of blood glucose level changes in a subject, wherein the different blood glucose level changes are selected among the type of nutrients, sport activities, stresses and fatigue or a combination thereof. The system is designed for accurately obtaining, measuring, registering and interpreting the pulse to determine the blood glucose level 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 blood glucose levels and discriminates between different sources of blood glucose level changes of the subject.