The Evoluent VerticalMouse 4 Small is for hands less than about 7 inches or 178 mm long from the tip of the middle finger to the wrist crease. Avoids forearm twisting for comfort and good health* The patented shape supports your hand in an upright neutral posture that generally avoids forearm twisting. Many users, including medical doctors, ergonomists and physical therapists, said the Evoluent VerticalMouse provides superior comfort and even relieved their wrist pain.* Comfortable and easy to use The shape is thoughtfully sculpted for uncompromised comfort and easy-to-reach programmable buttons. No finger contortions are needed to operate the buttons.