a user interface for receiving user input to enable tracking wherein the user input is received via a user interface that enables {HEAD ~ the user} to manually enable {TAIL ~ tracking}, to disable tracking or enable automatic triggering of tracking 
to manually enable
a user interface for receiving user input to enable tracking wherein the user input is received via a user interface that enables { HEAD ~ the user } to manually enable { TAIL ~ tracking } , to disable tracking or enable automatic triggering of tracking
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH