Time measurement is of great importance for science, technology, and commerce. Among the seven base units of the International System of Units, the second can be realized with the smallest uncertainty, currently reaching parts in 10<sup>16</sup>. Keeping track of the continuous accumulation of seconds allows the formation of time scales that serve as references for applications that require synchronization to national and international standards. This paper presents and discusses a multinational time scale developed for the Sistema Interamericano de Metrologia (SIM). This time scale, known as the SIM time scale, or SIMT, was developed to complement the official world time scale, Coordinated Universal Time, by providing real-time support to the operational timing systems within the SIM region. SIMT is generated from automated comparisons of time standards in North, Central, and South America, and is believed to be the first operational multinational time scale whose results are continuously published in real time via the Internet.
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