In trading on Wednesday, shares of the Vanguard Tax-Exempt Bond ETF ( VTEB) entered into oversold territory, changing hands as low as $51.21 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 Tax-Exempt Bond, the RSI reading has hit 28.5 — by comparison, the RSI reading for the S&P 500 is currently 62.6. A bullish investor could look at VTEB's 28.5 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), VTEB's low point in its 52 week range is $50.03 per share, with $52.88 as the 52 week high point — that compares with a last trade of $51.22. Vanguard Tax-Exempt Bond shares are currently trading off about 0.9% on the day.