The chromatic harmonica is bigger than the diatonic and has a lot more notes available on it. It is possible to play in all keys on the chromatic harmonica by using the slide, which is depressed (pushed in) to create extra notes. The most common chromatic harmonica has 12 holes and covers a range of three octaves. Although there are other keys, the C chromatic harmonica is the most common and is the one used in this book.
There are two rows of notes on the chromatic harmonica. The top row contains all the natural notes. The bottom row is blocked unless you press in the slide. When you depress the slide, it opens the bottom row which contains all the sharps and flats and at the same time blocks off the top row of notes. The use of the slide gives you 24 holes instead of 12.