the much shorter sounding length of the string in very high positions is a challenge for the right arm and bow in sounding the instrument effectively. The finer (and more expensive) an instrument, the better able it is to sustain good tone right to the top of the fingerboard, at the highest pitches on the E string. All notes (except those below the open D) can be played on more than one string. This is a standard design feature of stringed instruments; however, it differs from the piano, which has only one location for each of its 88 notes. For instance, the note of open A on the violin can be played as the open A, or on the D string (in first to fourth positions) or even on the G string (very high up in sixth to ninth positions). Each string has a different tone quality, because of the different weights (thicknesses) of the strings and because of the resonances of other open strings. For instance, the G string is often regarded as having a very full, sonorous sound which is particularly appropriate to late Romantic music. This is often indicated in the music by the marking, for example, sul G or IV (a Roman numeral indicating to play on the fourth string; by convention, the strings are numbered from thinnest, highest pitch (I) to the lowest pitch (IV). Even without an explicit instructions in the score, an advanced violinist will use her/his discretion and artistic sensibility to select which string to play specific notes or passages. Open strings If a string is bowed or plucked without any finger stopping it, it is said to be an open string. This gives a different sound from a stopped string, since the string vibrates more freely at the nut than under a finger. Further, it is impossible to use vibrato fully on an open string (though a partial effect can be achieved by stopping a note an octave up on an adjacent string and vibrating that, which introduces an element of vibrato into the overtones). In the classical tradition, violinists will often use a string crossing or shift of position to allow them to avoid the change of timbre introduced by an open string, unless indicated by the composer. This is particularly true for the open E which is often regarded as having a harsh sound. However, there are also situations