The American music industry used a standard of A 440 Hz in 1926,in instrument manufacturing. In 1936 the American Standards Association recommended that the A above middle C be tuned to 440 Hz. This standard was taken up by the International Organization for Standardization in 1955 . Why ? Because a long time ago musicians used different values for A thus a need for standards . As for ABCDEFG as opposed CDEFGAB why not DEFGABC ,EFGABCD ,FGABCDE ,OH No Now Iv'e gone modal on you ! I hate when I go modal,and don't get me started on the B/W thing .(lol) My first experience with that was my Dad playing guitar and he told me to only bang on the black keys and it would sound OK . Musta been F# he was in.