In trading on Monday, shares of the First Trust Energy AlphaDEX Fund ETF ( FXN) entered into oversold territory, changing hands as low as $20.50 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 First Trust Energy AlphaDEX Fund, the RSI reading has hit 29.2 — by comparison, the RSI reading for the S&P 500 is currently 76.0. A bullish investor could look at FXN's 29.2 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), FXN's low point in its 52 week range is $20.50 per share, with $29.84 as the 52 week high point — that compares with a last trade of $20.62. First Trust Energy AlphaDEX Fund shares are currently trading off about 2.2% on the day.