What "assets" are referred to in the Question?
SFAS is Statement on Financial Accounting Standards. You can get these from www.fasb.org
Link to SFAS 115
Yes that is correct.
For financial reporting per GAAP - the most common method used is straight line method-which is simple and easy to use. Other methods used could be double declining balance method or sum of the years digit method
for tax- MACRS(modified accelerated cost recovery system) is widely used.
For financial reporting per GAAP - the most common method used is units of production method.
In any case, I will attach a link to the worksheet which will provide you some information on the depreciation calculation under each of these methods-