Question: Shepherd Gate Clock was probably the first to display the solar time at which location in London?
Context: The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time (UTC) when standard time is in effect, and by subtracting six hours during daylight saving time (UTC−6).  The clock time in this zone is based on the mean solar time at the 105th meridian west of the Greenwich Observatory.  In the United States, the exact specification for the location of time zones and the dividing lines between zones is set forth in the Code of Federal Regulations at 49 CFR 71. Noon (also midday or noon time) is 12 o'clock in the daytime, as opposed to midnight.  The term 12 p.m. is commonly used, although it may be considered ambiguous.  Solar noon is when the Sun transits the local celestial meridian; this is when the sun is at its highest altitude in the sky, at 12 o'clock apparent solar time.  The local or clock time of solar noon depends on the longitude and date. The Shepherd Gate Clock is mounted on the wall outside the gate of the Royal Greenwich Observatory building in Greenwich, Greater London.  The clock, an early example of an electric clock, was a slave mechanism controlled by electric pulses transmitted by a master clock inside the main building.  The network of master and slave clocks was constructed and installed by Charles Shepherd in 1852.  The clock by the gate was probably the first to display Greenwich Mean Time to the public, and is unusual in using the 24-hour analogue dial. Universal Time (UT) is a time standard based on Earth's rotation.  It is a modern continuation of Greenwich Mean Time (GMT), i.e., the mean solar time on the Prime Meridian at Greenwich, London, UK.  In fact, the expression "Universal Time" is ambiguous (when accuracy of better than a few seconds is required), as there are several versions of it, the most commonly used being Coordinated Universal Time (UTC) and UT1 (see below).  All of these versions of UT, except for UTC, are based on Earth's rotation relative to distant celestial objects (stars and quasars), but with a scaling factor and other adjustments to make them closer to solar time.  UTC is based on International Atomic Time, with leap seconds added to keep it within 0.9 second of UT1. An equation clock is a mechanical clock which includes a mechanism that simulates the equation of time, so that the user can read or calculate solar time, as would be shown by a sundial.  The first accurate clocks, controlled by pendulums, were patented by Christiaan Huyghens in 1657.  For the next few decades, people were still accustomed to using sundials, and wanted to be able to use clocks to find solar time.  Equation clocks were invented to fill this need. Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London.  GMT was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time (UTC).  Today GMT is considered equivalent to UTC for UK civil purposes (but this is not formalised) and for navigation is considered equivalent to UT1 (the modern form of mean solar time at 0° longitude); these two meanings can differ by up to 0.9 s. Consequently, the term GMT should not be used for precise purposes. A circadian clock, or circadian oscillator, is a biochemical oscillator that oscillates with a stable phase relationship to solar time.  Such a clock's "in vivo" period, averaged over an earth year, is necessarily almost exactly 24 hours (the earth's current solar day).  In most living things, internally synchronized circadian clocks make it possible for the organism to coordinate its biology and behavior with daily environmental changes corresponding with the day–night cycle and derived diurnal behaviour patterns (e.g. crepuscular feeding). Solar time is a calculation of the passage of time based on the position of the Sun in the sky.  The fundamental unit of solar time is the day.  Two types of solar time are apparent solar time (sundial time) and mean solar time (clock time). The equation of time describes the discrepancy between two kinds of solar time.  The word "equation" is used in the medieval sense of "reconcile a difference".  The two times that differ are the "apparent" solar time, which directly tracks the diurnal motion of the Sun, and "mean" solar time, which tracks a theoretical mean Sun with noons 24 hours apart.  Apparent solar time can be obtained by measurement of the current position (hour angle) of the Sun, as indicated (with limited accuracy) by a sundial.  "Mean" solar time, for the same place, would be the time indicated by a steady clock set so that over the year its differences from apparent solar time would resolve to zero. The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time ().  During daylight saving time its time offset is eight hours ().  The clock time in this zone is based on mean solar time at the 135th meridian west of the Greenwich Observatory.
Answer: Royal Observatory