Welcome to the home of the Time and Frequency Metrology Working Group (TFMWG) of the Sistema Interamericano de Metrologia (SIM). SIM is a regional metrology organization that includes the national metrology institutes (NMIs) of the 34 member nations of the Organization of American States (OAS). In most cases, these NMIs are responsible for keeping the official time in their respective nations. The NMIs are located throughout North, Central, and South America, and the Caribbean Islands.
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 19 NMIs that currently participate in the SIMTN. The NMIs 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. They can also compare their time standard to UTC(USNO) as obtained through GPS, or to SIMT. To view the results of these comparisions, please select "Comparisons" from the menu on the left side of the display.