The coarse correction between UT1 and UTC transmitted by RWM. It is encoded in steps of 0.1 seconds.
An additional fine correction transmitted by RWM. It refines DUT1 in steps of 0.02 seconds.
UT1 is a time scale derived from the actual rotation of the Earth. UTC is the civil time scale based on atomic clocks.
RWM is a standard-frequency and time-signal radio station. This receiver monitors its transmission on 9.996 MHz.
RWM uses several different transmission segments. During the coded 1 Hz A1X signal, the receiver can determine second and minute timing and decode the DUT1/dUT1 Earth-rotation correction.
The station also transmits a 10 Hz A1N timing signal, carrier-only periods and station identification. Therefore, not every transmission segment contains the DUT1 code.
Atomic clocks run extremely uniformly, while the rotation of the Earth is not perfectly uniform. UT1 follows the actual orientation and rotation of the Earth, whereas UTC provides the world's civil time reference.
If UT1 − UTC is negative, Earth-rotation time is behind UTC. If it is positive, Earth-rotation time is ahead of UTC.
For example, a value of −0.02 s means that UT1 is currently about 20 milliseconds behind UTC. This does not by itself mean that the Earth is currently slowing down; that requires observing how UT1−UTC changes over time.
The second phase, minute phase, transmission mode and, during the RWM 1 Hz coded transmission, DUT1/dUT1 are derived from the received radio signal.
The decoded pulse structure used here does not provide a complete calendar date and hour. Absolute date/hour/minute context shown by this receiver therefore comes from the server system clock.