Posturite Wireless Penguin Mouse - Large (9820103) The vertical design encourages a neutral ergonomic alignment to protect against upper limb disorders Central 'bow-tie' switch allows for easy transition between right and left handed use Performance laser tracking and 4 DPI pointer speeds Plug & Play for Windows or Mac plus antimicrobial protection For correct size measure from the bottom of the palm to the tip of the middle finger. 0-6 = Small, 6-7 = Medium, 7+ = Large