Nice equation, makes your argument look more sciency.<p>Problem with it is that it ignores that physical things don&#x27;t follow standard accounting depreciation schedules.  Like I mentioned, you can&#x27;t make the assumption that physical resources like energy, labor, and materials flow through the economy like intangible &#x27;money&#x27;<p>The problem with your equation is that real things don&#x27;t degrade by X percent per year. Or more that the utility tends not to. For maintenance you usually have a fix part that is based on time and a variable part that depends on use.  And typically the the cost of depreciation occurs mostly at the end of life when you need to expend real resources to replace it. However if you don&#x27;t need to replace it then what? Bonus.