W R Grace Co is a global specialty chemicals company The following disclosure note was included in recent financial statements Change in Accounting Principle In the third quarter of 2008, Grace changed its method of accounting for the cost of its U S inventories from the last in first out method, o...

We report most voluntary changes in accounting principles retrospectively ...

W.R. Grace & Co.is a global specialty chemicals company. The following disclosure note was included in recent

Question:

W.R. Grace & Co. is a global specialty chemicals company. The following disclosure note was included in recent in Accounting Principle
In the third quarter of 2008, Grace changed its method of accounting for the cost of its U.S. inventories from the last-in/first-out method, or LIFO, to the first-in/first-out method, or FIFO. Grace decided to make this change in order to achieve a consistent inventory costing method for both U.S. and non-U.S. inventories. Grace has retrospectively restated prior periods' for all periods presented herein to account for all inventories using FIFO in compliance with generally accepted accounting principles.

Required:
Why does require W.R. Grace to retrospectively adjust prior periods' financial statement for this type of accounting change?

Financial Statements
Financial statements are the standardized formats to present the financial information related to a business or an organization for its users. Financial statements contain the historical information as well as current period’s financial... GAAP
Generally Accepted Accounting Principles (GAAP) is the accounting standard adopted by the U.S. Securities and Exchange Commission (SEC). While the SEC previously stated that it intends to move from U.S. GAAP to the International Financial Reporting Standards (IFRS), the...