In trading on Monday, shares of the Vanguard FTSE Europe ETF ( VGK) entered into oversold territory, changing hands as low as $46.85 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 Vanguard FTSE Europe, the RSI reading has hit 23.2 — by comparison, the RSI reading for the S&P 500 is currently 35.3. A bullish investor could look at VGK's 23.2 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), VGK's low point in its 52 week range is $40.12 per share, with $53.32 as the 52 week high point — that compares with a last trade of $46.96. Vanguard FTSE Europe shares are currently trading off about 2.1% on the day.