text: Characteristics related to useful life are that has an indeterminate or an unpredictable useful life because of the unusual manner in which it is used , improved , retired , modified , or maintained or is at a very high risk of being destroyed during use or of premature obsolescence .
  
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  The length of the useful life of a power-tool or computer depends on how well the owner properly maintains it , follows directions in its use and does not alter the product and so forth because any such changes can lead to a shorter useful life .