Parkinson's disease does not hold still for an appointment. Symptoms shift hour by hour as medication takes hold and wears off, which means a neurologist's twenty minutes with a patient captures one arbitrary slice of a moving picture, and the rest of it has to be reconstructed from memory. On October 28, the Boston- and Milan-based wearables company Empatica launched a product aimed squarely at that gap: WellPD, an FDA-cleared and CE-marked wrist-worn device and companion app that tracks Parki...