A bit of a rant but curious as well. We live in a microsecond HFT world, so why is it that we don't know the actual closing level of the S&P 500 until sometimes 4:15-4:20? On Friday, for example, the final closing number was almost a full point off the number that all the real-time feeds showed at 4:00, and we didn't show close to that final number until after 4:20. Does anyone know the mechanics of why the actual final number, or at least one that's within a tenth of a point, can't be determined and disseminated until so long after the actual close? I would think that it's nothing more than a simple math and computer science problem to gather up all the price feeds from everywhere a component stock trades, figure out the last one, and plug it into the weighting formula. I understand that you might occasionally have a busted trade, but this happens fairly consistently and at a magnitude that exceeds one or two busted trades on even the heaviest weighted index components. Thousands of HFT algos do this math millions of times a day, why can't the consolidated feed manage to pull it off?