The cost of a plant asset minus accumulated depreciation equals the asset’s book value.

Depreciation is a process of allocating the cost of a plant asset over its useful life.

Depreciation creates a fund to replace the asset at the end of its useful life.

Depreciation is based on the expense recognition principle. 

Property, plant and equipment assets are economic resources that have physical substance (tangible), are used in the operations of a business, and are not intended for sale to customers.