"BRP" is similar to other generic systems such as "GURPS", "Hero System" or "Savage Worlds" in that it uses a simple resolution method which can be broadly applied. "BRP" uses a core set of seven characteristics: Size, Strength, Dexterity, Constitution, Intelligence, Power, and Appearance or Charisma. From those, a character derives scores in various skills, expressed as percentages. These skill scores are the basis of play. When attempting an action, the player rolls percentile dice trying to get a result equal to or lower than the character's current skill score. Each incarnation of the "BRP" rules has changed or added to the core ideas and mechanics, so that games are not identical. For example, in "Call of Cthulhu", skills may never be over 100%, while in "Stormbringer" skills in excess of 100% are within reach for all characters. Scores can increase through experience checks, the mechanics of which vary in an individual game.