The keys are pressed one by one until {HEAD ~ the user} observes {TAIL ~ the desired effect} on the remotely controlled device 
The keys are pressed one by one until { HEAD ~ the user } observes { TAIL ~ the desired effect } on the remotely controlled device
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH