The PREM in this discussion will refer to any of the following. S&P Premium Nasdaq Premium Russell Premium Symbols here are based on Tradestation. The Premium is the difference between the futures and the cash index. The calculations are basically @SP.P - $INX = SP Premium, $NQIQX - $IQX = Nasdaq Premium, $ER2IUX - $IUX = Russell Premium. However, the actual calculation of the premium is a bit more involved._ The PREM is calculated tick by tick, every time that there is a trade for @SP.P, TS uses this value of @SP.P minus the previous value of the $INX to calculate the tick of the $spinx._The same procedure is used with the $INX._The values for the minute bar are taken from the tick data generated for the $spinx itself._Since not all stocks in the $INX open at the same time, the first few minutes of the $INX will be inaccurate._Consequently, the PREM will also be inaccurate until all stocks have opened._I adjust for this by using a custom session time that opens at 8:32._Additionally, since the futures close at 3:15 cst while the cash index closes at 3:00 cst. any PREM delivered after 3:00 cst is wrong.