Key signature key signatures showing sharps or flats on both octaves for notes which fall within the staff. An accidental is an exception to the key signature, applying only to the measure and octave in which it appears. Although a key signature may be written using any combination of sharp and flat symbols, the most common series of thirteen homogeneous key signatures—ranging from six flats to six sharps, with each successive flat or sharp placed on the note a perfect fifth below or above, respectively, the previous one—is assumed in much of this article. A piece scored using a single diatonic key
Key signature or a "sharp" key signature. The key signatures with seven flats () and seven sharps () are rarely used because they have simpler enharmonic equivalents. For example, the key of C major (seven sharps) is more simply represented as D major (five flats). For modern practical purposes these keys are (in twelve tone equal temperament) the same, because C and D are enharmonically the same note. Pieces "are" written in these "extreme" sharp or flat keys, however: for example, Bach's Prelude and Fugue No. 3 from Book 1 of The Well-Tempered Clavier BWV 848 is in C major. The modern