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