Micron Technology MERIDIAN 850 - Manual (Page 46)

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TruePoint™ Pointing Device
The red button, called the TruePoint™ embedded pointing device, works
like a joystick. Simply put a finger on it and tilt it the direction you want
the cursor on the screen to go. The harder you tilt, the faster it moves.
When you need to click on something, use the rectangular mouse buttons
(on top of the wrist rest) exactly as you would use the two buttons on a
mouse.
Chapter 4 - How to Use Your Meridian 850