In trading on Monday, shares of the Vanguard Extended Duration Treasury ETF (EDV) entered into oversold territory, changing hands as low as $115.70 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 Extended Duration Treasury, the RSI reading has hit 28.9 — by comparison, the RSI reading for the S&P 500 is currently 58.1. A bullish investor could look at EDV's 28.9 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), EDV's low point in its 52 week range is $100.00 per share, with $141.91 as the 52 week high point — that compares with a last trade of $116.02. Vanguard Extended Duration Treasury shares are currently trading off about 1.7% on the day.