Welcome to the home of the Time and Frequency Metrology Working Group (TFMWG) of the Sistema Interamericano de Metrologia (SIM). The SIM region covers North, Central, and South America, and the Caribbean Islands. The members of the SIM TFMWG are timing laboratories located at national metrology institutes and other designated institutions in the 34 member nations of the Organization of American States (OAS). In most cases, these timing laboratories are responsible for keeping the official time in their respective nations.
To support time and frequency metrology throughout the Americas, the SIM TFMWG maintains the SIM time scale (SIMT), the first continuously maintained multi-national ensemble time scale that is generated and published in real time (updated every hour). SIMT complements the world's official time scale, Coordinated Universal Time (UTC), by providing real time support to operational timing and calibration systems in the SIM region. The stability of SIMT is superior to most SIM local time scales and SIMT also provides a good approximation of UTC timing accuracy (±15 ns). The clock above displays SIMT, UTC, and your local time. It also shows the difference between local SIMT and the clock in the device you are using to view this site.
The map above shows the locations of the 23 timing laboratories that currently participate in the SIMTN. The laboratories that operate one or more cesium clocks and/or hydrogen masers contribute to the calculation of SIMT (the SIMT contributors are indicated by the white clocks on the map). 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 an undisciplined rubidium clock.
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 from servers located in Canada, Mexico, and the United States. Each SIMTN member can compare its national time standard to that of any other SIMTN member or to SIMT. To view the results of these comparisions, please select "Comparisons" from the menu on the left side of the display.