PREM is merely the difference between the SP futures index and the SP cash. It appears to lead the cash mostly because the futures contract gets reflected in the marketplace more quickly than the cash SP gets reflected on the ticker. The ONLY value (small one) I ever saw in the PREM was a huge discount to fair value on the opening. Then when the PREM starts to shrink to being less negative, it's often a sign the downside impulse is over... for the moment. If you want a similar play to try to catch a point or two, try fading the TICK when it's -1200 or so. It's not all that reliable, but still better than PREM.