Scroll Ring and Medium Ball - Spin the dial to move up and down web pages or documents with complete ease. The blue 40 mm ball has been specially designed with an absolute spherical, hard surface for precise tracking and control. KensingtonWorks Customization - Free downloadable software provides an even more personalized experience, giving you the ability to assign a wide variety of program functions to each of the 2 buttons, as well as adjusting cursor and scrolling speeds. Optical Tracking Technology - Provides precise cursor movement for superior accuracy so you can get where you want on the screen quickly with less hand movement, improving productivity and efficiency. Detachable Wrist Rest - Soft cushioning cradles the hand and wrist in ergonomic comfort for pain-free productivity during extended periods of activity on the computer. Ambidextrous Design - Works equally well for both right-handed and left-handed users to get the most out of their trackball. Plug and Play Installation - Quickly get clicking and scrolling with fast, simple installation through the reliable wired USB connection, plus it doesn’t need batteries. Compatible with Windows Vista and Mac OS X.