What are the yardage books Pro golfers carry around in their pockets?

Yardage books show distances to various targets on each hole, points of elevation, and a close-up of the green that shows detailed contours and yardages.

More about yardage books Pro golfers carry

The yardage book is an essential tool that all professional golfers use.

Caddies also carry one and spend hours on the golf course prior to their pro's arrival familiarising themselves with the book and the layout of the course.

Pros also add notes and details collected during practice rounds or past tournaments at the same course.