Difficulty level, roughly compared to ABRSM exam grades. 0 is beginner, 9 is advanced (beyond grade 8).
"This is the second book in the series of Piccolo! Piccolo!. Book 1 covers the introduction to the piccolo and prepares the development of the lower and middle registers. Book 2 is designed for the immediate to advanced player. The ideas in book 1 continue, this time exploring the entire range of the piccolo. Incorporating nineteenth century studies, solo and orchestral repertoire, the aim of book 2 is to provide a series of exercises and graded studies to develop a good facility across ALL registers." - Danielle Eden
Just Flutes Edition