We make discoveries about reality by examining the dierence between theory and practice. There is a well-developed theory about the dierence between theory and practice, and it is called "geophysical inverse theory". In this book we investigate the practice of the dierence between theory and practice. As the folklore tells us, there is a big dierence. There are already many books on the theory, and often as not, they end in only one or a few applications in the author's specialty. In this book on practice, we examine data and results from many diverse applications. I have adopted the discipline of suppressing theoretical curiosities until I find data that requires it (except for a few concepts at chapter ends).