There is also an iPhone App called "Dipsey Troller" for Jets/Dipsey's, etc, however, I have found that it isn't very accurate. I know Mark Romanack and Dr. Steve Holt who wrote those books (I bought a boat from them as well), and I will say that they put a ton of time and effort into gathering that data. Think about how long it would take, not to mention the gear needed to test all of those different scenarios and set-ups. It isn't the cost of publishing the book, it is the time/effort and cost of getting the data to put into it. I think it is well worth the money to purchase one. Especially when you consider what you spend in gas, maintenance, storage, tackle, etc, etc, to know how deep your stuff is running. I keep a copy of the Great Lakes version in my glove-box on the boat and use it almost every time we go out.