After 4 years of using a machine acquired at a cost of $15,000, Miller Construction Company determined that the original estimated life of 10 years had been too short and that a total useful life of 12 years was a more reasonable estimate. Explain briefly the method that should be used to revise the depreciation program, assuming that straight-line depreciation has been used and the machine has no residual value. Assume that the revision is made after recording depreciation and closing the accounts at the end of 4 years of use.