jerky movement of the mouse with ubuntu - how to fix it

$ xinput  (search for id corresponding to external mouse -> 9 )
$ xinput --list-props 9  
$ xinput --set-prop 9 "Device Accel Constant Deceleration" 2

It's also possible to calibrate acceleration and threshold by using xset command

$ xset q | grep -A 1 Pointer
$ xset m 18/10 0