Editing Key signature (section)

=== Unusual signatures ===
{{further information|Anhemitonic scale#Modes of the ancohemitonic heptatonic scales and the key signature system}}

The 15 key signatures that form diatonic scales are sometimes called ''standard key signatures''. Other scales are written either with a standard key signature and use accidentals as required, or with a nonstandard key signature. Examples of the latter include the E{{music|b}} (right hand), and F{{music|#}} and G{{music|#}}<!--yes, sharp--> (left hand) used for the С diminished (С [[octatonic scale|octatonic]]) scale in Bartók's ''Crossed Hands'' (no. 99, vol. 4, ''[[Mikrokosmos (Béla Bartók)|Mikrokosmos]]''); the B{{music|b}}, E{{music|b}} and F{{music|#}}<!--yes, sharp--> used for the D [[Phrygian dominant scale]] in [[Frederic Rzewski]]'s ''God to a Hungry Child''; and the E{{music|b}} and D{{music|b}} (right hand) and the B{{music|b}}, A{{music|b}}, G{{music|b}} (left hand) in [[György Ligeti]]'s ''Galamb Borong'' (no. 7 from the second book  of the ''Études pour piano''), and B{{music|b}}, E{{music|b}}, D{{music|b}}, G{{music|b}} (both hands) in ''Pour Irina'' (no. 16 from the same work's third book).

There are also examples of conflicting standard signatures, as in:
* no. 3 of [[Sergei Prokofiev]]'s ''[[Sarcasms (Prokofiev)|Sarcasms]]'', op. 17 (three sharps in the right hand, and five flats in the left hand)
* and four numbers of [[György Ligeti|Ligeti]]'s ''[[Études (Ligeti)|Études pour piano]]'':
** no. 1 from the first book (none in the right hand, and five sharps in the left hand)
** no. 10 from the second book (''Der Zauberlehrling''; none in the right hand, and five flats in the left hand in bars 67–87)
** no. 11 from the second book (''En Suspens''; five flats in the right hand and none in the left hand, with the opposite later on)
** no. 12 from the second book (''Entrelacs''; none in the right hand and five flats in the left hand, with the opposite later on)

No sharps or flats in a key signature can indicate that the music is in the key of C major&nbsp;/ A minor, or that the piece is [[Musical mode|modal]] or [[atonality|atonal]] (does not have a key signature). An example is Bartók's [[Piano Sonata (Bartók)|Piano Sonata]], which has no fixed key and is highly chromatic.