This document discusses various methods for calculating depreciation of physical assets. It defines depreciation as the decrease in value of an asset over time due to factors like wear and tear, technological changes, and economic conditions. The purpose of depreciation is to allocate the original cost of an asset over its useful life. Common depreciation methods include straight-line, declining-balance, and sum-of-the-years digits, with each method calculating depreciation differently, especially in early versus later years of an asset's life. Key terms discussed include salvage value, service life, and book value.