A vibrato system on a guitar is a mechanical device used to temporarily change the pitch of the strings. They add vibrato to the sound by changing the tension of the strings, typically at the bridge or tailpiece of an electric guitar using a controlling lever, which is alternately referred to as a whammy bar, vibrato bar, or incorrectly as a tremolo arm. The lever enables the player to quickly and temporarily vary the tension and sometimes length of the strings, changing the pitch to create a vibrato, portamento, or pitch bend effect. Instruments without a vibrato have other bridge and tailpiece systems.