Hacker News Reader

>But never mind. What if we take my picture and rotate it 180 degrees? Then we get a new chord! This trick is called a tritone substitution.

I know tritone subtitution from music theory, and trying to grok this explanation. What does the "roation by 180 degrees" represent in this case?

He means turn the circle of fifths 180 degrees. In other words, move the chord up a tritone (six half-steps).

The drawing looks like a circle of half steps, not a circle of fifths.

It seems that the article would be clearer if the 180 degree rotation were to put F# at the top of the drawing.

Yes, good observation. Why would that help, though? No matter what's at the top, you're turning the whole thing halfway around.