I calculate the zone by using implied volatility from the futures to solve for a one standard deviation price range. Then multiply that by .75 for the bottom and 1.5 for the top of the zone. To pick direction I simply use the Ichimoku Kinko Hyo. When the price is above the kumo I'm short, when its below the kumo I'm long. The success rate should hover around 50% but you'll find that your average wins are normally bigger than your average losses. I close it at the end of the New York session