All the notes that make up the interval parts of a musical scale contain 12 half steps. These are the finite parts within the Chromatic Scale. Think of it as a measurement ruler to measure the distance between notes. We measure the distance between notes in half steps instead of inches like a ruler (Ex.1).
Instead of 1-12 it’s 1-7 and we have 5 between accidental numbers b2, b3, b5, b6, b7 none between 3&4, 7&1 (Ex.2).
In music scale theory we use numbers for intervals as an easier way to measure the distance or steps between notes in a music scale or in a music chord. If we count higher than 7 we go into the next octave and 1 starts over again as the 1 in the square of this chromatic scale on the guitar scale fretboard (Ex.1). This applies to music scale theory and playing scales on guitar. In chord theory harmony we use interval numbers higher than (7) called compound intervals this will be explained later in future lesson.
Every music scale has scale formula (1, 2, 3, 4, 5, 6, 7 is the Major Scale Ex.4), (1, b3, 4, 5, b7 is the Minor Pentatonic Scale Ex. 5) the bordered numbers. The notes in music are taken from the first 7 letters of the alphabet A-G with 5 accidentals that each have with 2 names (incrementing A to A# sharps & decrementing B to Bb flats) C#-Db, D#-Eb, F#-Gb, G#-Ab. There is no accidental notes between B-C, and E-F (Ex.3). This can be a challenge to learn because we have to break away from our old mind associations of how we uses letters in the alphabet as well as number in counting.
The Guitar Analyzer Diagrams below can give a better perspective to understand the interval ruler. You see dynamically how the bordered numbered notes below overlay the static notes measuring the distance between the notes. This creates easy to recognize guitar scale shapes and is an aid for guitar players who play by ear. These guitar fingering diagrams can be create very easy with just a few mouse clicks with the Guitar Analyzer Software.
Ex.1 Ex.3 Ex.4 Ex.5