If you move 7 steps from center C in a 12 o'clock direction followed by a
single step in a 2 o'clock direction you will land on an F whose fractional
relation to C is within one ppm (part per million) of the ET relation. This tiny difference, which
I have christened Hirsh's comma (H), means that you can with a clear conscience draw your
ET line between these two notes. It is expressed by: