So how can we use the circle to notate the key signature? We know that C major has no key signature and that G on the clockwise side has one sharp and that F on the anticlockwise side has one flat and that it goes in sequence, e.g. D major has two sharps, A major has three sharps, Bb major has two flats, Eb major has three flats and so on.

I showed how to figure out which notes are sharped and flatted for each scale by plotting it out. But can we shortcut the process by using the Circle? Yes, we can!

To determine the flats, drop back two notes on the circle counterclockwise. G major gets one sharp so drop back two spaces on the circle to F major and that is the note that gets sharped in G major. Or you can draw a line from G to the center of the circle and go back 60 degrees counterclockwise. Moving to D major, which has two sharps, drop back 60 degrees to C and that is the next sharp so D major has two sharps—F and C. And so on. Remember that the sharps and flats accumulate so add the ones previous.

For flats, we look at the note on the opposite side of the circle. So the note opposite F is B so that is the note that gets flatted in F major. Or we can drop back (or move forward) 180 degrees to find the flats. The next note of the circle is Bb and will get two flats. We already know that one will be B and the other is 180 from Bb which is E so Bb major is flatted at B and E. And so on.

Remember sharps and flats accumulate and always follow a specific order and it bears repeating: The order of the sharps in the key signature is FCGDAEB while the order of the flats in the key signature is BEADGCF so one is simply the reverse of the other.

And I would like to add that you can go around the circle in either direction but the clockwise direction is counting in 5ths. The counterclockwise direction is counting in 4ths. 4ths and 5ths are simply inverses of each other and 99% of all music is dependent on them. As one writer put it--the 4th and 5th are the twin pillars of music (he must have been a Freemason).