This book began as a paid contract for a publishing company. I was writing it in my sparetime, but the publisher and I had different opinions about where the book was going.
It sat on my hard drive after we went our separate ways for almost a year until I got around to updating it and self-publishing it myself.
In the spirit of Open Source I decided to offer it at no cost, with the option to purchase it as well and release it under a Creative Commons License.
Honestly, I'm staggered and humbled by the number of people who have actually paid not only the suggested price of the book, but often chose to pay more. I've also been contacted by readers thanking me and telling me that they have found this book useful and helpful. This was the entire goal of the project - share and provide information to others.
If you notice any typos and want to submit errata, I welcome it. You can use the discussion mechanism where you purchased it, or the issue pages since the entire text is hosted at Github. You can also contact me directly by email. I'm pretty easy find on Google + and Twitter @bhosmer.
- Ben Hosmer