| Beats are also the result of two frequencies destructively and constructively interfering. The corresponding peaks and valleys in total signal strength form beats, with each cycle one beat. This phenomenon can be easily observed when watching a piano or guitar tuner; the electronic devices used for this purpose visually display the beats generated by playing a reference tone along with the corresponding piano key or guitar string. The slower the beats, the closer the frequencies are to identical; when the beats have been eliminated, the string is tuned.
tdent informs me that when tuning tempered fifths by ear, one "looks for a certain number of beats rather than eliminating them entirely." Thanks! | 
