The Apple Pro Mouse was introduced in 2000 along with the G4 Cube. This mouse dropped the rubber ball used for tracking in all previous Apple mouse designs and replaced it with a solid-state LED optical sensor. The design of the mouse appeared to feature no buttons, but the entire mouse surface allowed for a single click. The shape of the mouse was an an elongated rectangle with two round sides (replacing the previous round design).
The surface of the original version of this mouse was crystal clear acrylic with a base insert in black that matched the keyboard that shipped with it. This version replaced the black insert with a white insert, and the bottom of the mouse used a translucent white screen.
The Apple Pro Mouse also included a ring to allow for three different click force settings on the underside of the mouse.
The successor to the Apple Pro Mouse was called the Apple Mouse and the ring on the underside that controlled the click settings was removed. The bottom of the mouse was replaced with opaque white plastic and a light gray gliding surface (shown below).
Source: Wikipedia.com
