DRS Corporation changed the way it depreciates its computers from the sum-of-the-year's digits method to the straight-line method beginning January 1, 2011, DRS also changed its estimated residual value in computing depreciation for its office building. At the end of 2011, DRS changed specific subsidiaries constituting the group of companies for which its consolidated financial statements are prepared.

Required:

1) For each accountant change DRS undertook, indicate the type of change and how DRS should report the change. Be specific

2) Why should companies disclose change in accounting principles?