In trading on Friday, shares of the Proshares Short FTSE China 25 ETF ( YXI) entered into oversold territory, changing hands as low as $29.9601 per share. We define oversold territory using the Relative Strength Index, or RSI, which is a technical analysis indicator used to measure momentum on a scale of zero to 100. A stock is considered to be oversold if the RSI reading falls below 30.In the case of Proshares Short FTSE China 25, the RSI reading has hit 28.5 — by comparison, the RSI reading for the S&P 500 is currently 33.6. A bullish investor could look at YXI's 28.5 reading as a sign that the recent heavy selling is in the process of exhausting itself, and begin to look for entry point opportunities on the buy side. Looking at a chart of one year performance (below), YXI's low point in its 52 week range is $29.77 per share, with $39.18 as the 52 week high point — that compares with a last trade of $29.96. Proshares Short FTSE China 25 shares are currently trading down about 1% on the day.