Scientific pitch notation creates a linear pitch space in which an octave spans 12 semitones, where each semitone is the distance between adjacent keys of the piano keyboard. Distance in this space corresponds to musical pitch distance in an equal-tempered scale; 2 semitones being a whole step, 1 semitone being a half step. An equal-tempered semitone can also be subdivided further into 100 cents. Each cent is semitone or octave. This measure of pitch allows the expression of "microtones" not found on standard piano keyboards. The notation is sometimes used in the context of meantone temperament, and does not always assume equal temperament
Octave standard 88-key piano keyboard, while the C an octave higher is C. The notation "8" or "8" is sometimes seen in sheet music, meaning "play this an octave higher than written" ("all' ottava": "at the octave" or "all' 8"). "8" or "8" stands for "ottava", the Italian word for octave (or "eighth"); the octave above may be specified as "ottava alta" or "ottava sopra"). Sometimes "8" is used to tell the musician to play a passage an octave "lower" (when placed under rather than over the staff), though the similar notation "8" ("ottava bassa" or "ottava sotto") is also used.