more than a means to regulate play. In less abstract games (Risk), turns obviously denote the passage of time, but the amount of time is not clear, nor important. In simulation games, time is generally more concrete. Wargames usually specify the amount of time each turn represents, and in sports games a turn is usually distinctly one 'play', although the amount of time a play or turn takes can vary. Some games use player turns where one player gets to perform their actions before another player can perform any on their turn (Monopoly and chess would be classic examples). Some use game turns, where all players contribute to the actions of a single turn (board-game simulations of American football tend to have both players pick plays and then determine the outcome; each 'play' or 'down' can be considered a turn). Some games have 'game turns' that consist of a round of player turns, possibly with other actions added in (Civilization plays with a series of player turns followed by a trading round in which all players participate). In games that are meant to be some sort of simulation, the on/off nature of player turns can cause problems and has led to a few extra variations on the theme. The semi-simultaneous turn allows for some reactions to be done during the other player's turn. The impulse-based turn divides the turn into smaller segments or impulses where everyone does some of their actions at one time, and then reacts to the current situation before moving on to the next impulse (as seen in Star Fleet Battles or Car Wars). In some games, not all turns are alike. Usually, this is a difference in what phases (or different portions of the turn) happen. Imperium Romanum II for instance, features a "Taxation and Mobilization Phase" in every third turn (month), which does not occur in the other turns. Napoleon has an unusual variation on the idea, where every third player turn is 'night turn' where combat is not allowed. Even in real-time computer games, there are often certain periodic effects. For instance, a wounded character in World of Warcraft will gradually recover health while out of combat. The rate of recovery is calculated from the character's statistics and applied per "tick" as a lump sum, so a character would gain ten health per tick, instead of one every tenth of a tick. These periodic