Here at Zacks, we focus on our proven ranking system, which places an emphasis on earnings estimates and estimate revisions, to find winning stocks. But we also understand that investors develop their own strategies, so we are constantly looking at the latest trends in value, growth, and momentum to find strong companies for our readers.Of these, value investing is easily one of the most popular ways to find great stocks in any market environment. Value investors use tried-and-true metrics and fundamental analysis to find companies that they believe are undervalued at their current share price levels.On top of the Zacks Rank, investors can also look at our innovative Style Scores system to find stocks with specific traits. For example, value investors will want to focus on the "Value" category. Stocks with high Zacks Ranks and "A" grades for Value will be some of the highest-quality value stocks on the market today.One stock to keep an eye on is Gerdau (GGB). GGB is currently holding a Zacks Rank of #2 (Buy) and a Value grade of A.Investors should also note that GGB holds a PEG ratio of 0.38. This popular metric is similar to the widely-known P/E ratio, with the difference being that the PEG ratio also takes into account the company's expected earnings growth rate. GGB's PEG compares to its industry's average PEG of 0.47. Over the last 12 months, GGB's PEG has been as high as 5.36 and as low as -7.74, with a median of 0.60.Another valuation metric that we should highlight is GGB's P/B ratio of 1.75. 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 solid versus its industry's average P/B of 2.36. Over the past 12 months, GGB's P/B has been as high as 1.97 and as low as 0.67, with a median of 1.24.Finally, investors should note that GGB has a P/CF ratio of 8.27. This metric takes into account a company's operating cash flow and can be used to find stocks that are undervalued based on their solid cash outlook. GGB's P/CF compares to its industry's average P/CF of 12.53. Over the past year, GGB's P/CF has been as high as 11.14 and as low as 5.74, with a median of 8.69.These figures are just a handful of the metrics value investors tend to look at, but they help show that Gerdau is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, GGB feels like a great value stock at the moment.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 Gerdau S.A. (GGB): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research