Comparison of the Multinational SIM Time Scale to UTC and UTCr

The Sistema Interamericano de Metrología (SIM) is one of the world's five major regional metrology organizations (RMOs) recognized by the International Committee for Weights and Measures (CIPM). To allow SIM National Metrology Institutes (NMIs) to track the performance of their time and frequency standards in almost real-time, the SIM Time and Frequency Metrology Working Group (SIM TFWG) established the SIM Time Network (SIMTN) in 2005. As of 2019, 26 SIM nations participate in the SIMTN. Since 2008, the SIM TFWG has produced the SIM Time Scale (SIMT), a multinational ensemble computed every hour from time difference measurements collected by the SIMTN every 10 min. The SIMT, the first continuously maintained multinational ensemble time scale that is generated and published in near real-time, complements the world's official time scale, Coordinated Universal Time (UTC), by providing real-time support to the operational timing and calibration laboratories at SIM NMIs. The SIMT provides a real-time approximation of UTC with a timing uncertainty near 10 ns. In this article, we present an SIMT evaluation based on data from November 2016 to June 2018 by comparing SIMT performance to that of UTC and rapid UTC (UTCr). We discuss the performance differences between the SIMT, UTC, and UTCr and how that time scales are used in the SIM region.