Through the course of the book you have learnt many different notes in two different playing positions (first position and second position or cross harp). There are various musical ways of describing all these notes and relating them to keys. There are two different ways to approach this lesson. You may wish to study each scale and description in detail, or you may wish to use it basically as a reference while continuing to develop your playing by ear and asking questions of other musicians. There are many good harmonica players who have very little knowledge of music theory. However, it is the author’s belief that you can get a lot further if you understand the sounds you are making and how to transfer them to harmonicas in other keys.