Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Unnecessary

This is a waste of money. If you want to know how to use a pendulum well there's really nothin' to it. And there's a wealth of information on it on the internet if you really want to get creative. So the book does nothing for you. In fact it's a little annoying to think of someone trying to charge for information they sure didn't invent. This is an ancient practice after all.The cards you can make yourself (yes they'll work fine if they don't look fancy)and to your own specifications.Which only leaves the pendulum itself. It'd be much cheaper to buy a lightweight plumb bob instead.