In trading on Friday, shares of the FTSE Greece 20 ETF ( GREK) entered into oversold territory, changing hands as low as $19.99 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 FTSE Greece 20, the RSI reading has hit 27.3 — by comparison, the RSI reading for the S&P 500 is currently 45.0. A bullish investor could look at GREK's 27.3 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), GREK's low point in its 52 week range is $14.11 per share, with $25.76 as the 52 week high point — that compares with a last trade of $20.00. FTSE Greece 20 shares are currently trading down about 3.5% on the day.