Difficulty level, roughly compared to ABRSM exam grades. 0 is beginner, 9 is advanced (beyond grade 8).
The Taggarts have done it again! This is such a great book for all those pupils who can't/won't play scales. The tunes are all based on simple scales and arpeggios but the backing tracks are so good that you hardly notice. Hence scales become all gain and very little pain. Brilliant!