Which is the most reliable method of determining depreciation charges for equipement or machinery purchasing?

I would use Amortization....

https://en.wikipedia.org/wiki/Amortization

Amortization (or amortisation; see spelling differences) is the process of reducing, or accounting for, an amount (usually a financial debt) over a period according to a plan.

According to GAAP (General Accepted Accounting Practices) the popular method is diminishing value method by subracting a percentage off each year for the depreciation value. In general it is between 5 and 10% depending on the equipment or machinery. The amount in use can have an effect on the depreciation value of the goods, for instance a company vehicle that clock up many kilometers per year. In vehicles they normally use a formulae that combines distance traveled withn a year period. Facory machinery is often also depreciated in a hourly usage per annumn basis formulae. 

Diminishing balance method is the most reliable and the most applicable method for the machinery and equipment depreciation charges

 equipment or machinery purchasing?  ... In general it is between 5 and 10% depending on the equipment or machinery. The amount in use can ..

Diminishing balance method is the most reliable and the most applicable method for the machinery and equipment depreciation charges

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 equipment or machinery purchasing?  ... In general it is between 5 and 10% depending on the equipment or machinery. The amount in use can ...