Aroon up and Aroon down are the two components that comprise the Aroon indicator. The notion is that an asset is trending up when a stock is trading near the high of its range. Aroon up is used to measure the strength of the uptrend, while Aroon down is used to measure the strength of the downtrend. Many traders will watch for a cross above the zero line to suggest the beginning of a new uptrend. Conversely, a cross below zero would indicate the start of a downtrend. Readings near zero suggest that a security may be trending sideways and that this period of consolidation could continue.