Because of all the time and effort required to fill in the details, Greller said, he lives in dread of losing his Masters book. It would be like losing a computer file that was not saved on your hard drive. “It’d be less stressful to lose my passport, absolutely,” he said.

The value of the books was driven home recently when Jeff Ghim, who is caddying here for his 21-year-old son, Doug, lost the yardage book he had painstakingly padded with notes over three months of research.

The book fell from a pocket of his long-sleeved overalls on Monday. His heart dropped, he said.

“Fifteen years my son’s dreamed of playing here,” Jeff Ghim said, “and I lose the directions.” How could he replicate three months’ worth of notes in two days?

Thankfully, he got the book back. Someone turned it into the caddie headquarters the next day, and Ghim, with book in pocket, guided his son, a Masters rookie, to low-amateur honors.

Image An image from a modern greens book detailing the contours of a green at Hazeltine National during the 2016 Ryder Cup there. Mark Long, the president of Tour Sherpa, provided course field guides for the event. He typically sells his greens books for $150 each.



Credit... Mark Long/Tour Sherpa

Yardage books have been around since at least the 1950s, when the future P.G.A. commissioner Deane Beman, then a junior golfer, sketched crude models for his own use. In the 1970s, the books proliferated as professional players and caddies, in search of a legal edge, turned to the course field guides compiled by pioneers like Mark Long, who has followed the high-tech path. He supplies his greens books to caddies for $150 apiece.