The Initial Balance (IB) is a measurement of the extent the auction has gone one way or another during the first hour since the open. It is defined as the high and low of the first hour of trading. This is the traditional definition that you will find. Just like with everything else, my view on this is not really “traditional”. I pay attention to not only the high and low of the first hour of business (this is usually when the main order flow happens), but I also pay attention to how it is happening. Is it a straight shot down like what occurred on this day?
Generally, if the price discovery process is fast like it was on the link above, then ES will go into a wide rotation up and will provide more scalping opportunities. If it grinds down the range in the same time period, it will likely have very little rotational action and will have a steady seller pushing it through the IB-low in a choppy fashion.