Impairment vs Downward revaluation

What is the difference between asset Impairment and downward revaluation? Under US GAAP is the following valid after a revaluation The new Book Value of the asset = Historical Cost - Accumulated Depreciation - Loss due to downward revaluation. thanks!

Impairment is when carrying value (historical cost - accumulated depreciation) > future cash flows. The write down has a twist… Impairment write down = carrying value - discount future cash flows This will decrease earnings, ROE, and ROA in the current period. After that they will increase since you don’t have the depreciation expense.

Also, under US GAAP, assets CANNOT be revalued upward unless they are being held for sale. Under IFRS assets CAN be revalued upward up their fair value. The asset revaluation erases the previous write down and any additional revaluation increases equity (other comprehensive income).