While the proven Zacks Rank places an emphasis on earnings estimates and estimate revisions to find strong stocks, we also know that investors tend to develop their own individual strategies. With this in mind, we are always looking at value, growth, and momentum trends to discover great companies.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 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 Arch Coal (ARCH). ARCH is currently holding a Zacks Rank of #1 (Strong Buy) and a Value grade of A. The stock has a Forward P/E ratio of 6.40. This compares to its industry's average Forward P/E of 8.21. Over the past year, ARCH's Forward P/E has been as high as 12.13 and as low as 6.11, with a median of 8.82.We should also highlight that ARCH has a P/B ratio of 2.26. The P/B is a method of comparing a stock's market value to 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 3.61. ARCH's P/B has been as high as 3.37 and as low as 2.16, with a median of 2.73, 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. This is a prefered metric because revenue can't really be manipulated, so sales are often a truer performance indicator. ARCH has a P/S ratio of 0.65. This compares to its industry's average P/S of 1.69.These figures are just a handful of the metrics value investors tend to look at, but they help show that Arch Coal is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, ARCH 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 Arch Coal Inc. (ARCH): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research