takes place application_number US 6672598 A description fig1 is an underside view of a typical mouse illustrating the ball and roller system architecture a typical computer mouse 9 is viewed from underneath showing various standard components trackballs have a similar structure a removable cover plate 11 physically holds a mouse ball 15 in a spherical cavity when mouse ball 15 is inserted into mouse 9 with cover plate 11 snapped firmly into place mouse ball 15 makes contact with a plurality of calibrated rollers in this example there are two rollers 13a and 13b for providing directional input in a typical mouse at least one tension device such as spring 17 is used to effect 100 physical contact between mouse ball 15 and the rollers in some cases a third spring loaded idler roller is provided to urge the ball into the directional input rollers the constant physical contact between mouse ball 15 and rollers 13a and 13b enables smooth and accurate directional input during operation as long as the system is clean smooth and accurate cursor movement is essential to successful cursor manipulation object manipulation in drawing applications and for other purposes as previously described in the background section contamination of the form of lint dust food particles and the like eventually corrupts the ball roller system and degrades the performance of the device a track ball is essentially a mouse device with the ball roller system on the upper surface instead of the lower instead of rolling across a surface as with a conventional mouse a track ball is stationary with cursor movement effected by physically manipulating the ball directly the ball roller system is basically identical with both types of pointer devices with an exception that a ball used with.