The Fair Value, although calculated using the previous days closing prices is basically constant for that next day's trading. Assuming there is 2 points added to the spot price of the S&P 500 index (to get to "fair value"), then if the futures are trading at 5 points over the spot price, then you see a 3 point "premium" which will have to either translate to an upswing in the underlying (500 stocks), or an immediate downturn in the futures. Since the floor traders and institutions are constantly hedging, this result is consistent.