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Passive ultra-high-frequency (UHF) radio-frequency identification (RFID) has developed rapidly over the past two decades. In 2012 alone, about 4 billion tags were sold worldwide . Manufacture and deployment at this volume has been made possible by minimizing tag cost, making a strong disincentive for the added expense of RF performance testing. As a result, performance metrics and test methods are not yet unified or generally adopted. Large customers in industry and government, however, wish to compare products with parameters like read range and inventory rate, so this problem is attracting more attention, and test standards are improving. This article discusses the history, state of the art, and some future challenges in this rapidly evolving area of study. In particular, we consider two metrics for digitally modulated backscatter of passive UHF RFID tags and how tests can be simplified for reduced costs. Examples for some 860-960 MHz commercial tags and applications are given to illustrate the method.