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Written by Oleksandr Gavenko (AKA gavenkoa), compiled on 2017-01-30 from rev ccaa2f364422+.

Music.

Music scale.

Scale is any set of musical notes ordered by fundamental frequency or pitch.

Scale ordered by increasing pitch is an ascending scale, and a scale ordered by decreasing pitch is a descending scale.

The distance between two successive notes in a scale is called a scale step.

For Western music with 12 tones in octave used several definition of steps:

  • semitone, half step is 2^(1/12)
  • whole step, whole tone, major second is 2^(2/12)

Chromatic scale is a musical scale with twelve pitches, each a semitone above or below another. On a modern piano or other equal-tempered instrument, all the semitones have the same size (100 cents). In other words, the notes of an equal-tempered chromatic scale are equally spaced.

Diatonic scale (or heptatonia prima) is a scale composed of seven distinct pitch classes: 2–2–1–2–2–2–1.

Minor scale: 2-1-2-2-1-2-2.

Pentatonic major scale: 1, 2, 3, 5, 6. Pentatonic minor scale: 1, ♭3, 4, 5, ♭7.

The eight degrees of the diatonic scale are also known by traditional names:

  • 1st degree – Tonic (key note)
  • 2nd degree – Supertonic
  • 3rd degree – Mediant
  • 4th degree – Subdominant
  • 5th degree – Dominant
  • 6th degree – Submediant
  • 7th degree – Leading tone
  • 8th degree – Tonic (Octave)

Intervals names:

The notes of a scale are numbered by their steps from the root of the scale.

https://en.wikipedia.org/wiki/Scale_%28music%29
Often, especially in the context of the common practice period, most or all of the melody and harmony of a musical work is built using the notes of a single scale, which can be conveniently represented on a staff with a standard key signature.
https://en.wikipedia.org/wiki/Common_practice_period
Common-practice harmony is almost always derived from diatonic scales and tends to follow particular chord progressions that have withstood the test of time.