Horizontal lines appear on the oscillator chart at the 70 and 30 values. Traders often use those lines to generate buy and sell sig­nals. We already know that a move under 30 warns of an over­sold condition. Suppose the trader thinks a market is about to bottom and is looking for a buying opportunity. He or she watches the oscillator dip under 30. Some type of divergence or double bottom may develop in the oscillator in that oversold region. A crossing back above the 30 line at that point is taken by many traders as a confirmation that the trend in the oscilla­tor has turned up. Accordingly, in an overbought market, a crossing back under the 70 line can often be used as a sell signal