If you’re watching professional golfers on tour and wonder what that booklet is tucked into their back pockets or entrusted to their caddies, that’s a yardage book. All elite courses have them, and they include detailed overviews of every hole on the course, including distance markers to help a player get a sense of what club to use and what lies ahead.
Golfers don’t usually carry the USGA “Rules of Golf” with them, as rules officials wait on every hole to answer specific questions or settle disputes.