Since the introduction of "Commander's Edition" the rules have been organized with lettered major chapters, followed by a number to indicate a major rule. Then follows a decimal, and a series of numbers indicating the breakdown into subsections. (For instance, (D6.683) is the third subsection of (D6.68) Disrupted Fire Control, which is the eighth subsection of (D6.6) Active Fire Control, which is the sixth section of (D6.0) Fire Control Systems, which is the sixth rule in (D0.0) Combat.) Chapter R is an exception; as it is a listing of every ship type in the game, the number after the decimal is a sequental number identifier. e.g., (R2.12) is the Police Cutter, the eleventh Federation ship in the game (as (R2.1) is background information). Occasionally, a chapter might have sub-chapters, which are indicated with two letters.