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.Looking at the history of these trends, perhaps none is more beloved than value investing. This strategy simply looks to identify companies that are being undervalued by the broader market. Value investors use a variety of methods, including tried-and-true valuation metrics, to find these stocks.Zacks has developed the innovative Style Scores system to highlight stocks with specific traits. For example, value investors will be interested in stocks with great grades in the "Value" category. When paired with a high Zacks Rank, "A" grades in the Value category are among the strongest value stocks on the market today.One stock to keep an eye on is Contura Energy (CTRA). CTRA is currently sporting a Zacks Rank of #1 (Strong Buy), as well as an A grade for Value.Investors should also recognize that CTRA has a P/B ratio of 0.34. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. This company's current P/B looks solid when compared to its industry's average P/B of 0.48. CTRA's P/B has been as high as 0.55 and as low as 0.05, with a median of 0.16, over the past year.Value investors also frequently use the P/S ratio. This metric is found by dividing a stock's price with the company's revenue. Some people prefer this metric because sales are harder to manipulate on an income statement. This means it could be a truer performance indicator. CTRA has a P/S ratio of 0.07. This compares to its industry's average P/S of 0.2.These are just a handful of the figures considered in Contura Energy'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 CTRA 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 Contura Energy, Inc. (CTRA): Free Stock Analysis Report To read this article on Zacks.com click here.