Ergo 3-Button Srial -PS/2 Trackball with built in wristrest, still wrapped in plastic. Microsoft Windows Compatible. Thumb button and two finger buttons Built-in wrist rest Programmable third button 3 rugged tactile click micro-switch kiysSerial or PS/CompatiblePrecise movement with opto-mechanical technologyEasy-to-clean rollers with removable ballUp to 4000dpi dynamic resolution