The Price Relative indicator compares the performance of one security to another with a ratio chart. This indicator is also known as the Relative Strength indicator or Relative Strength Comparative. Often, the Price Relative indicator is used to compare the performance of a stock against a benchmark index, S&P 500, BIST:XU100 etc.
Chartists can also use the Price Relative to compare the performance of a stock to its sector or industry group. This makes it possible to determine if a stock is leading or lagging its peers. The Price Relative indicator can also be used to find stocks that are holding up better during a broad market decline or showing weakness during a broad market advance. (Source: stockcharts)
This also can be used for Trend Identification and Bullish/Bearish Divergences.