In trading on Tuesday, shares of the Proshares Short Financials ETF ( SEF) entered into oversold territory, changing hands as low as $21.532 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 Financials, the RSI reading has hit 29.0 — by comparison, the RSI reading for the S&P 500 is currently 71.3. A bullish investor could look at SEF's 29.0 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), SEF's low point in its 52 week range is $21.532 per share, with $31.09 as the 52 week high point — that compares with a last trade of $21.56. Proshares Short Financials shares are currently trading down about 0.8% on the day.