BPM is idiosyncratic in that it transmits UT1 time between minutes 25 through to 29 and 55 through to 59, which creates an odd click-beep effect when heard below a stronger time signal station such as WWV.
Greenwich Mean Time (GMT) is mean solar time at the Royal Greenwich Observatory in Greenwich, London, England, which by convention is at 0 degrees geographic longitude.
Noon Greenwich Mean Time is not the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich) because of Earth's uneven speed in its elliptic orbit and its axial tilt.
On 1 January 1972, GMT was replaced as the international time reference by Coordinated Universal Time (UTC), maintained by an ensemble of atomic clocks around the world.
Greenwich Mean Time (GMT) is the mean solar time at the Royal Greenwich Observatory in Greenwich near London in England, which by convention is at 0 degrees geographic longitude.
Because of the Earth's uneven speed in its elliptic orbit, this event may be up to 16 minutes off apparent solar time (this discrepancy is known as the equation of time); but this is averaged out over the year through the use of the mean sun.
Nowadays, the official clock time is measured by atomic clocks and is known as Coordinated Universal Time (UTC).
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