Usually a companys book value and Tangible Book Value per Share may not reflect its true value. The assets may be carried on the balance sheets at the original cost minus depreciation. This may underestimate the true economic values of the assets. It also may over-estimate their true economic value because the assets can become obsolete.
For financial companies such as banks and insurance companies, their assets may be reported in current market value of the assets owned. Book values of financial companies are more accurate indicator of the economic value of the company.