Penguin Ambidextrous Vertical Mouse Wired Medium Naturally Comfortable The vertical alignment encourages a more ergonomic operating position. Ambidextrous Design Central 'bow-tie' switch allows for easy transition between right and left handed use. Precision performance laser Provides accurate tracking on typical work surfaces.Adjustable 400, 600, 800 or 1200 dpi settings.Encourages fast and precise operating movements. Precision scroll wheel For fast, accurate document scrolling including an auto-scroll feature. The Penguin mouse is available in three sizes. To choose the correct one for you, measure your hand from the first crease on your wrist to the tip of your middle finger.SMALL0-16cm(0-6ins)MEDIUM16-18cm(6-7 ins)LARGE18cm +(7 ins +)