According to the National Research Council of Canada:
Time accuracy superior to telephone time accuracy is available throughout Canada and in many other parts of the world by means of NRC's radio time signals broadcast continuously from short wave radio station CHU. If corrections are made for the propagation delay from CHU to the user, and for delays in the user's receiver, an accuracy of better than 1 ms can be obtained. Signal availability at a user's location depends on ionospheric conditions. CHU also broadcasts a time code which can be decoded with common computers and modems.
Three frequencies are used: 3330, 7850, and 14670 kHz. The transmission mode, upper single sideband with carrier re-inserted, provides time signal service without requiring a special SSB radio, and also provides three standard frequencies. The frequencies are derived from one of a trio of closely synchronized atomic clocks located at the transmitter site. Three clocks are employed to permit majority logic checking. CHU time signals are also derived from these clocks. The clocks at the CHU transmitter site, about 20 km from NRC's time laboratory, are compared daily with the NRC primary cesium clocks.
Normally CHU's emission times are accurate to 10^-4 s, with carrier frequency accuracy of 5x10^-12, compared to NRC's primary clocks, which are usually within 10 microseconds and 1x10^-13 compared to UTC.
CHU's shortwave time signals can easily be heard in the U.S. and many other countries due to the typically long-range propagation of shortwave signals.