Use xinput to configure Kensington Orbit Optical Trackball
 

I need to use "xinput" to enable middle button and scrolling on this Kensington Orbit Optical mouse of 2 buttons.
The way to do this is xinput --list to obtain the device name or id number. When this is done it returns 3 devices: Virtual core pointer (which is presented as tho it might be a overall device name, Master) with an id of 2, Vertual core XTEST pointer with an id of 4, and ImPS/2 Generic Wheel Mouse with id = 11 (both called Slaves). I see other types of Kensington's use a slave name. I need just 1 to create a emulated middle button but which? I need a reason to select 2, 4, or 11 for this as I have had enough gotchas for a month of Sundays.