Sudoku puzzle books are like the bowls of porridge that Goldilocks found at the cottage of the Three Bears. Some are too cold (easy), and others too hot (difficult). 
With “Craig’s Sudoku Book” series of 10 puzzle books, you should be able to find a Sudoku book for you that’s “just right.”
Each of the ten books in the series is assigned an overall difficulty level based on the quantity and difficulty level of puzzles it contains. Using the table here (on the back of every book in the series), you can see the difficulty level you will face in each book and choose appropriately.