There is no default binding to the slew button press in switch. I have it set to centre my trackir when pressed quickly and also to freeze trackir when pressed for about quarter of a second or more. Using AutoHotkeys to do this.
So basically, set it to whatever you want.
There is also a push in switch on the 4-way hat switch on the right hand side of the right throttle as well, incase you didn't know it was there. Its a bit fiddly to press in though without accidentally pressing one of the four direction switches.
Regards,
Milli