Since depreciation is an allocation of an asset's cost based on the estimated useful life, you should not assume that the depreciation is an indicator of what's occurring to the asset's market value. For example, a building in an excellent location may be increasing in value even though depreciation is taken. The present market value might be three times the original cost and yet the accumulated depreciation is now equal to the asset's cost—meaning its book value is $0.
The amount reported in Accumulated Depreciation merely reports the total amount of an asset's cost that has been sent over to the income statement as Depreciation Expense since the asset was acquired.
Learn Accounting: Gain unlimited access to our seminar videos, flashcards, visual tutorials, exams, business forms, and more when you upgrade to PRO.