Welcome to the website of the Time and Frequency Metrology Working Group (TFMWG) of the Sistema Interamericano de Metrologia (SIM). This site allows you to view the results of interlaboratory comparisons conducted through the SIM Time Network (SIMTN), with new results published every 10 minutes. It is also the home of the SIM time scale (SIMT), believed to be the first multi-national ensemble time scale that is generated and published in real time. SIMT is updated hourly. It complements Coordinated Universal Time (UTC) by providing real time support to operational timing and calibration systems in the SIM region. SIMT is sufficiently stable to measure the stability of most SIM local time scales and provides a good approximation of UTC timing accuracy (±15 ns).
The map below shows the locations of the 19 laboratories that participate in the SIMTN. The white clocks represent laboratories that operate cesium clocks and contribute to the calculation of SIMT. The green clocks represent laboratories that operate rubidium clocks that are automatically disciplined to agree with SIMT. The purple clocks represent laboratories that operate either a GPS disciplined clock or a free running rubidium clock.