Your friend Tom Smith has decided to expand Smith Sales Company. He has acquired an expansion loan and purchased $500,000 of plant assets as part of the expansion. Tom values your advice and requests your help in properly depreciating the plant assets. Tom has paid you well for your advice and you readily accept the challenge.

Explain the different methods that can be used to calculate depreciation including: Straight-line, Double declining balance, Units of production & Sum of years digits.