Why not just use the MACRS tax depreciation schedule that the IRS uses? Look up the asset class, and depreciate it using the correct MARCS schedule by asset class. For GAAP, some companies use straight-line to boost EPS, thus the discrepancy from tax, shown as deferred tax liabilities on the B/S.
I figured that is what you were trying to do. So the question I would ask I guess is what is management’s incentive to be so aggresive in depreciating their fixed assets?