Book value is the net value of a firm's assets found on its balance sheet, and it is roughly equal to the total amount all shareholders would get if they liquidated the company.
Obsolescence is the state of being which occurs when an object, service, or practice is no longer maintained, required, or degraded even though it may still be in good working order.
A deferred tax liability is a tax that is assessed or is due for the current period but has not yet been paid—meaning that it will eventually come due.
The function of a depreciation provision is to make a company's balance sheet more accurately reflect the current value of the investments it has made in fixed assets over time.