Ok - I'll start on the explanation...

"MAJOR SCALES have the following intervals in them - root note - root+2 - root+4 - root+5 - root+7 - root+9 - root+11 - root note again (ie root+12)."

We start with root - root + 5 - (root + 5)+5 [that's the 2nd of the scale] - ((root + 5)+5)+5 [that's the 6th of the scale] - and so it goes.

The problem with doing it that way is that it doesn't all add up when you get back to the alleged 'root' again - that's called a 'ceasura', or a break, and is why 'just intonation' was superseded by various systems that attempted to spread the 'differences' - resulting in the modern 'root 12 impermanent' system.


... but that all is probably far more than you thought you really wanted to know... :-P

:-)