The BIGtrack has a 3 inch trackball which makes it the largest trackball available. The large ball requires less fine motor control than a standard trackball and it is ruggedly built. It has a left and a right mouse and special Drag Lock. * Features a 3-inch yellow ball and has two blue buttons (for left and right mouse clicks) located behind the trackball to avoid unwanted clicks and special Drag Lock feature for ease of access. * Compatible with a Windows or Macintosh computer that has a USB or PS/2 port