In trading on Friday, shares of the Proshares Short Real Estate ETF ( REK) entered into oversold territory, changing hands as low as $24.59 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 Real Estate, the RSI reading has hit 29.6 — by comparison, the RSI reading for the S&P 500 is currently 60.1. A bullish investor could look at REK's 29.6 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), REK's low point in its 52 week range is $23.20 per share, with $28.51 as the 52 week high point — that compares with a last trade of $24.59. Proshares Short Real Estate shares are currently trading down about 0.7% on the day.