In trading on Thursday, shares of the iShares FTSE NAREIT Real Estate 50 Index Fund ETF ( FTY) entered into oversold territory, changing hands as low as $39.50 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 iShares FTSE NAREIT Real Estate 50 Index Fund, the RSI reading has hit 27.6 — by comparison, the RSI reading for the S&P 500 is currently 44.2. A bullish investor could look at FTY's 27.6 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), FTY's low point in its 52 week range is $37.57 per share, with $46.46 as the 52 week high point — that compares with a last trade of $39.54. iShares FTSE NAREIT Real Estate 50 Index Fund shares are currently trading off about 2.2% on the day.