This is a great intro book for the novice looking to understand more about GPS. It is a good start for someone wanting to purchase their first GPS receiver, or someone who already has a receiver but wants to learn more about it. The info is presented in a clear, logical way, but it tends to be a bit basic for more advanced users. I was hoping to learn more about differential GPS and post processing of data for improved accuracy. The book gave general discriptions of both, but not a lot of detail. For instance, it did not explain, as I later discovered, that low-cost consumer receivers are not compatible with post processing. The compilation of commercial receivers is a bit dated, but most of the rest of the book is still very topical.