independent chip model. Basically it's a method that SNG players use to figure out what their equity in the tournament is. Since the way that you buy-in and cash-out in a tournament is different than in a cash game, the chips you have in your stack are not directly proportional to a dollar amount the same way they are in a cash game. Rather, the worth of each chip changes depending on how much you have, how many players are left, how many chips they have, etc.
so I would google independent chip model for a more-in depth look, also you can check this thread: [old link~tb]