CVN Chart, page-299

BHP is a classic example over the years of a stock that always closes the gap. Whether the share price has gapped up or down in the past. Take a look at the gap up in price on the 11th April this year from 29.10 the day before. Sure as the sun will come up tomorrow eventually the price of BHP will retrace and fill that gap. Could go to $45 first, who knows but eventually the momentum will turn and the price will fall, might take a couple of months or a couple of years but it will happen. And because this phenomenon does occur traders will position themselves around these gaps as either entry or exit points.