Michael Port (2006). “Book Yourself Solid: The Fastest, Easiest, and Most Reliable System for Getting More Clients Than You Can Handle Even if You Hate Marketing and Selling”, p.94, John Wiley & Sons
Michael Port, Jocelyn Wallace (2013). “Book Yourself Solid Illustrated: The Fastest, Easiest, and Most Reliable System for Getting More Clients Than You Can Handle Even If You Hate Marketing and Selling”, p.24, John Wiley & Sons