The reward book can be banked, unlike many other experience-giving items. The book will give experience based on your skill level when it is used, not when it was earned. The amount of experience received from the reward book is , where is the level of the skill on which it is being used, is the wave completed (or trolls killed in defending) and is the total number of waves (20 on easy, 7 on hard, 1500 in defend). Note that for Invention, any experience received is halved.