A Musical Scale consists of a collection of music notes with pre-defined Pitch distances. Notes with Frequency difference of two times are said to be an Octave apart.
In a commonly used 'Equal Tempered' scale, the Notes are divided equally into several parts, usually 12. Equal means that the ratio of frequencies of adjacent intervals is fixed – 1.059 approx (12th root of 2 for mathematically inclined)
Each Step is referred to as a Semitone (S) and 2 steps as Tone (T)
The Note A above middle C with frequency of 440 Hz is used as Tuning Standard in Western Music.
The Beauty of Diatonic Scale lies in the fact that these notes sound so good, when played in ascending or descending order or in various other patterns. Indeed Diatonic Scale has been used as a backbone framework over various genres of music across the world.
Checkout entire presentation 'An Introduction to Music' below.