In trading on Friday, shares of the PowerShares National AMT-Free Municipal Bond Portfolio ETF ( PZA) entered into oversold territory, changing hands as low as $24.97 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 PowerShares National AMT-Free Municipal Bond Portfolio, the RSI reading has hit 27.1 — by comparison, the RSI reading for the S&P 500 is currently 53.4. A bullish investor could look at PZA's 27.1 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), PZA's low point in its 52 week range is $24.31 per share, with $25.94 as the 52 week high point — that compares with a last trade of $25.00. PowerShares National AMT-Free Municipal Bond Portfolio shares are currently trading down about 0.6% on the day.