This book contains mnemonics and other tips to better perform a specific mental task, and its words are charged with magic. If you spend 24 hours over a period of 3 days or fewer studying the tome and practicing its instructions, you gain proficiency in the Intelligence, Wisdom, or Charisma-based skill (such as History, Insight, or Intimidation) associated with the book. The tome then loses its magic, but regains it in ten years.