source files: xbtp.[ch]
(XBTP-PEN-THRESHOLD [ NEW-THRESHOLD ] )
The Wacom has an optional stylus which is pressure sensitive. The xbtp.c driver needs to know how hard the user should have to push before a 'click' is generated, and uses a 0.0->1.0 parameter to control this.
XBTP-PEN-THRESHOLD returns the previous value of this parameter; if NEW-THRESHOLD (a float) is provided, it is clipped to the range [0,1] and becomes the new value of this parameter.