Stockopedia explains P/B...
This is a key metric for value investors, whereas growth investors typically believe that book value reveals very little about a company's prospects for future performance.
The price / book value ratio rarely falls below 1.0. As with most ratios, it varies a fair amount by industry (companies that require more infrastructure capital will usually trade at P/B ratios much lower than, for example, consulting firms). P/B ratios are often used to compare banks, because most assets and liabilities of banks are constantly valued at market values.
A company that can't make an ROE greater than its cost of capital may be expected to have a low price to book. Therefore, look for a low PBV combined with a high ROE and low default risk.