Mark Long never thought he would become a professional golf caddie back when he was a finance student at the University of Maryland, where he played on the golf team. Two years after Long graduated, his former coach, Fred Funk, set out to join the PGA Tour. Long agreed to carry his bag, accompanying Funk when he made it to the Tour. In 1991, Long teamed up with Nolan Henke, whose victory at a tournament in Arizona earned him invitations to The Masters, the British Open and overseas events. And so a career was forged. Caddies serve as trusted advisers to the golfers they work with, helping them plot their approach to each hole. Many rely on detailed course maps called yardage books to guide their strategies. After becoming frustrated by the yardage books available through the Tour, Long, 45, set out to make his own. At first, he used a survey wheel to take measurements for his maps, which proved inaccurate. Then he tried a handheld laser with limited results. Long eventually called a surveying store, where he found a helpful owner who walked him through the latest technology. Taking a leap of faith, he bought expensive equipment and set about raising the standards for yardage books. Today, the self-taught Long uses six different computer programs, many designed for engineers, and global-positioning devices to create his yardage books. His work helped him become a stronger caddie. "Measuring angles and understanding how yardages work has been good for me," Long said. "When I used to work for Nolan, I'd tell him, 'Watch this: The guy's going to come up five yards short.' He would, and Nolan would just love that."