Yardage books are essential for Tour caliber golfers and useful for ordinary players. A number of courses provide yardage books for their patrons. You can use a yardage book to supplement the other ways to measure the distances between two points on the course -- GPS devices, rangefinders and the traditional red, white and blue stakes or metal fairway disks that mark the 200-, 150- and 100-yard distances from the middle of the fairway to the middle of the green. Good yardage books offer a more detailed way to calculate distances between various landmarks on the course -- for example from the tee to an out-of-bounds marker or from the fairway to a bunker protecting the green. Caddies of professional golfers carry yardage books that they supplement to calculate precise distances and determine, for example, that their golfer has 156 yards rather than 155 yards to the pin.
Measure the length of your stride with a tape measure or ruler to determine what kind of stride -- bigger, smaller or regular -- you need to adopt on the golf course to walk off yardages. Use your adjusted stride so each step corresponds to 1 yard.
Using the diagram for the hole in the yardage book, walk off the yards from your ball to a landmark. For example, if your drive is 15 yards short of a landmark that's 185 yards from the center of the green, you're faced with a 200-yard shot to the center of the green.
Adjust the distance for factors such as the terrain and wind. For example, an uphill shot will not travel as far as a shot on flat terrain. Adjust the distance for the position of the flagstick. Golf courses indicate the flagstick position in different ways. At some, the color of the flag indicates the depth of the flag. Other courses have the daily flag position card in the golf cart. Still others indicate the flag depth via a small flag or ball on the stick -- higher for a deeper position and lower for a front-green position.
Avoid potential hazards in your path by calculating distances from landmarks in the yardage book. For example, if the flag and green are 200 yards away, and a landmark bunker protecting the left side of the green is listed in your yardage book at 15 yards to the center of the green, you subtract 15 from 200 to determine you have to hit a shot that travels at least 185 yards in the air to clear the bunker.
Apply the calculations from the yardage book to play smart golf and lower your score. Are you a talented enough golfer to fire directly at the pin from 200 yards away and hit the shot far enough to clear the bunker? If so, fire away. If not, the best play is likely to the right side of the green to avoid the bunker if your shot comes up short.