Published in BattleTech Compendium: The Rules of Warfare.
Rules Level 1
Published in BattleTech, Third Edition, and generally dealt with the Technology Level first introduced in the Age of War along with one piece of equipment developed in the Succession Wars Era. Rules Level 1 equipment is on the referenced page.
Rules Level 2
Published in BattleTech Compendium: The Rules of Warfare, and dealt with Standard and Advanced Rules. This book included Age of War, Succession Wars era equipment, and Technology introduced in Technical Readout: 2750 and Technical Readout: 3050. Rules Level 2 equipment is on the referenced page. The Game Play and Construction Rules delt with in this book constitute the level of game play that most BattleTech players experienced.