I've never met two caddies who keep a yardage book the same way. If you handed mine to another caddie, he'd probably hand it right back. "It's in your language," he'd say.
A yardage book isn't just a map. It's a memory. On one page I don't just see that the bunker begins at 247 yards. I remember the college kid who tried to carry it with a three wood because he wanted to impress his future father-in-law. He didn't.
The numbers stay the same. The stories change everything.