Regulator Clock Showing Mean and Solar Time

Solar time (the time determined by a sundial) and mean time (the time shown on a clock) agree only four times a year and can vary by as much as sixteen minutes. The difference between these two times is known as the equation time. This “equation” clock automatically adjusts the relationship of the two minute hands throughout the course of the year. When the gilt-brass minute hand is adjusted to the time shown on a sundial, the blued-steel minute hand will automatically indicate the correct mean time. One of the finest French clockmakers of the eighteenth-century, Robert Robin received several royal appointments during the reign of Louis XVI. This elegant design, which he introduced around 1780, was his most successful model.

Source: Vignon, Charlotte. The Frick Collection Decorative Arts Handbook. New York: The Frick Collection/Scala, 2015.