Working assets (26) are equipped with ID tags (56) that respond to interrogations from interrogators (50). Each interrogated tag (56) sends response codes that identify the tag (56) and working asset (26), can describe an amount of use experienced by the working asset (26), and can describe unused capacity...http://www.google.com.au/patents/US5664113?utm_source=gb-gplus-sharePatent US5664113 - Working asset management system and method
