Kensington Orbit Optical Trackball

The comfort of a mouse -- the benefits of an optical trackball
Control your cursor with a simple touch of the finger! The highly accurate Orbit? Optical is as easy to use as a regular mouse, but it stays in one place saving you valuable desk space. The precise optical tracking mechanism is also resistant to dust, reducing the need for regular trackball cleaning

   
Features
DiamondEye optical technology for precise tracking and cursor control
The comfort of a mouse and the fingertip control of a trackball
Uses less arm movement and desk space than a conventional mouse
USB and PS/2 connectivity for greater compatibility
Specifications

Optical trackball with medium sized ball and two mouse buttons
Cord Length: 6ft
Metallic silver and black
PS/2 and USB connectivity (for PCs and USB Macs)
System Requirements
PC-Windows? 98, Me, 2000, or XP with USB port
PC-Windows? 95, 98, Me, NT, 2000, or XP with PS/2 compatible mouse port
Macintosh? with OS 10.1.5 or later
USB Macintosh? with OS 8 & 9, device will only function as a 1-button mouse

The comfort of a mouse -- the benefits of an optical trackball