In trading on Tuesday, shares of the Proshares UltraPro Short S&P500 ETF ( SPXU) entered into oversold territory, changing hands as low as $17.9101 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 UltraPro Short S&P500, the RSI reading has hit 28.5 — by comparison, the RSI reading for the S&P 500 is currently 71.3. A bullish investor could look at SPXU'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), SPXU's low point in its 52 week range is $17.9101 per share, with $46.29 as the 52 week high point — that compares with a last trade of $17.99. Proshares UltraPro Short S&P500 shares are currently trading down about 2.2% on the day.