interaction between {HEAD ~ the cam follower} and {TAIL ~ the cam curvilinear surface} creating a plurality of pushbutton equilibrium states 
interaction between { HEAD ~ the cam follower } and { TAIL ~ the cam curvilinear surface } creating a plurality of pushbutton equilibrium states
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH