I am not 100% for you, in case you have something in your control panel set up different or changed. The default should be button 1 & 2 are usually set unconfigured unless you apply them to some function.
The button "+" and "-" are for sensitivity in rotation, zooming, panning, etc.
The Panel Button would open the 3D software panel or the "Control Panel" for the 3DConnexion drivers/software isntalled on your computer to change the properties and functions of your 3D mouse. The "Fit" button is for "Fit All Geometry" in CATIA. It's usually on the toolbar with your primary views or swap between show/noshow button.
