Investors with an interest in Instruments - Control stocks have likely encountered both Nanometrics (NANO) and Woodward (WWD). But which of these two stocks is more attractive to value investors? We'll need to take a closer look to find out.There are plenty of strategies for discovering value stocks, but we have found that pairing a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system produces the best returns. The proven Zacks Rank emphasizes companies with positive estimate revision trends, and our Style Scores highlight stocks with specific traits.Nanometrics and Woodward are both sporting a Zacks Rank of # 2 (Buy) right now. This system places an emphasis on companies that have seen positive earnings estimate revisions, so investors should feel comfortable knowing that these stocks have improving earnings outlooks. But this is just one piece of the puzzle for value investors.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their current share price levels.The Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.NANO currently has a forward P/E ratio of 20.95, while WWD has a forward P/E of 23.94. We also note that NANO has a PEG ratio of 1.75. This popular figure is similar to the widely-used P/E ratio, but the PEG ratio also considers a company's expected EPS growth rate. WWD currently has a PEG ratio of 1.86.Another notable valuation metric for NANO is its P/B ratio of 2.27. 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. By comparison, WWD has a P/B of 4.16.These metrics, and several others, help NANO earn a Value grade of B, while WWD has been given a Value grade of C.Both NANO and WWD are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that NANO is the superior value option 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 Nanometrics Incorporated (NANO): Free Stock Analysis Report Woodward, Inc. (WWD): Free Stock Analysis Report To read this article on Zacks.com click here.