GAAP uses the lower of cost or market method for valuing inventories. Cost is simply historical cost - the amount that the company paid to purchase the inventory. Market is more difficult to compute. Under GAAP, market is the middle of three figures:
1 - The ceiling, which is the net realizable value. Net realizable value is selling price less anticipated costs to complete and sell the inventory.
2 - The floor, which is the ceiling less a normal profit expected to be earned.
3 - Replacement cost, which is the amount the company would have to pay to replace the inventory.

IFRS simplifies the computation by valuing inventory at lower of cost or net realizable value (NRV). Although the term is not used in IFRS, NRV is equal to the ceiling under GAAP.
Another significant difference between IFRS and GAAP relates to the recovery of losses. GAAP does not permit you to recover losses recognized from writing inventory down to market. IFRS, however, does permit a loss to be reversed should the inventory regain its value in a subsequent period

Fixed assets is another area of major differences between GAAP and IFRS

GAAP requires the use of historical cost. IFRS allows companies a choice - either stay with historical cost or revalue your assets. Revaluation is simply the process of restating your assets to current market value.
Initial revaluations increases are charged to other comprehensive income, decreases to the income statement. Subsequent adjustments going the opposite way first offset the initial revaluation.
In other words if the first revaluation was an increase and the next is a decrease, apply the decrease against other comprehensive income to the extent of the increase. Any excess goes to the income statement.
Assets accounted for under the cost method are still subject to impairment rules. Impairments are charged to expense. Similar to inventory writedowns, companies are allowed to recover, but only to the extent of the original adjusted basis computed as if the impairment had never incurred.
What I mean is depreciation. After an impairment, annual depreciation charges decrease based on a lower basis. When a recovery is identified, you have to figure out what the adjusted basis would have been if depreciation was computed based on the original basis.

Research and development is expensed under GAAP

IFRS allows you to capitalize development, but not research. There are a set of rules that define when something is research and when it is development. My summary of the rules is, the development phase begins when:
1 - we prove that the project can be completed (technological feasibility), and
2 - we can make money (economic feasibility)
When determining economic feasibility, look for indications of a marketing plan being developed.