Here at Zacks, our focus is on the proven Zacks Rank system, which emphasizes earnings estimates and estimate revisions to find great stocks. Nevertheless, we are always paying attention to the latest value, growth, and momentum trends to underscore strong picks.Of these, perhaps no stock market trend is more popular than value investing, which is a strategy that has proven to be successful in all sorts of market environments. Value investors rely on traditional forms of analysis on key valuation metrics to find stocks that they believe are undervalued, leaving room for profits.In addition to the Zacks Rank, investors looking for stocks with specific traits can utilize our Style Scores system. Of course, value investors will be most interested in the system's "Value" category. Stocks with "A" grades for Value and high Zacks Ranks are among the best value stocks available at any given moment.One stock to keep an eye on is Rio Tinto (RIO). RIO is currently sporting a Zacks Rank of #1 (Strong Buy), as well as an A grade for Value. The stock is trading with a P/E ratio of 7.10, which compares to its industry's average of 11.10. RIO's Forward P/E has been as high as 12.96 and as low as 6.96, with a median of 9.16, all within the past year.Investors should also recognize that RIO has a P/B ratio of 2.01. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. This stock's P/B looks attractive against its industry's average P/B of 3.36. RIO's P/B has been as high as 2.21 and as low as 1.02, with a median of 1.75, over the past year.These are just a handful of the figures considered in Rio Tinto's great Value grade. Still, they help show that the stock is likely being undervalued at the moment. Add this to the strength of its earnings outlook, and we can clearly see that RIO is an impressive value stock right now.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Rio Tinto PLC (RIO): Get Free Report To read this article on Zacks.com click here.