A capodastra (or capo) is used to change the pitch of open strings. Capos are clipped onto the fret board with the aid of spring tension, or in some models, elastic tension. To raise the guitar's pitch by one semitone, the player would clip the capo onto the fret board just below the first fret. Their use allows a player to play in different keys without having to change the chord formations they use. Because of the ease with which they allow guitar players to change keys, they are sometimes referred to as "cheaters". Classical performers are known to use them to enable modern instruments to match the pitch of historical instruments such as the renaissance lute.