Ball; )

I prefer trackballs mice for my PC (for lack of space on my desk). I have had for over 10 years a Microsoft Explorer (not looking for is no longer manufactured) very good bill, but begins to age.
Alrs I opted for the Kensington because it has a scroll wheel that can scroll pages. (Attention to detail prohibitive!). This 'wheel' is actually the gray wheel hard plastic that surrounds the ball.
I preferred the ball from the Explorer because larger, and its more precise wheel and two buttons front page 'and' back page 'handy when surfing.
But hey, it no longer exists (Messrs. Constructors .. why ??) so I 'content' of this model that fills his office, and still satisfying ergonomics. (I tried a model with ball-count but did not suit me .. then he must test if possible before buying because so it is a personal matter;) Pictured ball to lead the thumb to great, but giving my case it soon became an ordeal.)
Unlike my previous trackball, Kensington is symmetrical, it should therefore also for left.