In trading on Tuesday, shares of the Proshares Short MidCap400 ETF ( MYY) entered into oversold territory, changing hands as low as $16.70 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 MidCap400, the RSI reading has hit 28.7 — by comparison, the RSI reading for the S&P 500 is currently 67.8. A bullish investor could look at MYY's 28.7 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), MYY's low point in its 52 week range is $16.70 per share, with $21.44 as the 52 week high point — that compares with a last trade of $16.72. Proshares Short MidCap400 shares are currently trading down about 0.7% on the day.