A computer mouse is a device that usually measures around 3 inches that is used as input to control a pointer on a computer screen. Variations include a trackpoint and motion sensing devices.
Computer mice usually have two features, something on the bottom (a laser, or trackball)to sense motion and move the pointer around on the screen, and at least one button to click. Modern mice also have scroll wheels on top to help scroll and right-click buttons which provide a variety of different functions.
Computer mice were invented in 1964 by Douglas Engalbart. 
Accuracy depends on:
- Size of the optical sensor -- larger is generally better, assuming the other mouse components can handle the larger size. Sizes range from 16 x 16 pixels to 30 x 30 pixels.
- Refresh rate -- it is how often the sensor samples images as you move the mouse. Faster is generally better, assuming the other mouse components can process them. Rates range from 1500 to 6000 samples per second.
- Image processing rate -- is a combination of the size of the optical sensor and the refresh rate. Again, faster is better and rates range from 0.486 to 5.8 megapixels per second.
- Maximum speed -- is the maximum speed that you can move the mouse and obtain accurate tracking. Faster is better and rates range from 16 to 40 inches per second.