Palmer Corp. is evaluating the appropriate accounting for the following items under ASPE:
1. Management has decided to switch from the FIFO inventory cost formula to the weighted average inventory cost formula for all inventories.
2. When the year-end physical inventory adjustment was made for the current year, the controller discovered that the prior year's physical inventory sheets for an entire warehouse were mislaid and excluded from last year's count.
3. Palmer's Custom Division manufactures large-scale, custom-designed machinery on a contract basis. Management decided to switch from the completed-contract method to the percentage-of-completion method of accounting for long-term contracts because they are now able to estimate the progress toward completion (whereas they were not able to measure this before).
Explain whether each of the above items is a change in accounting principle, a change in estimate, or an error.