I purchased this book from Amazon for my IPad this weekend for $10. I recommend it. I have operated our IFD540 for several years and still learned a few things. It has info in an easier to understand format than the IFD manual and has several graphics for visual awareness. Anyone using the Avidynne Navigators will benefit. There is also a hard copy available for $44.95. The kindle reader app for an IPad is free and saved me $35 plus I could enjoy the book this weekend. I will probably be looking for other books to read over the next couple of weeks until the Covid 19 concerns decrease. Any suggestions will be appreciated.