Jean-Baptiste Lependu, maître in 1782.
Messen, active in Paris in the second half of the 18th Century. Although little is known about him, the inscription on the dial would suggest he worked for one of the brothers of the King, the comte d'Artois or the comte de Provance.
Edme-Portail Barbichon was a specialist émallieur, recorded in the late 18th Century (see J.-D. Augarde, Les Ouvriers du Temps, Geneva, 1996, p. 101).
The difference between solar and mean time is known as the equation of time. The invention of the pendulum in 1658 brought a far greater degree of accuracy to timekeeping and it became very apparent to the new owners of these clocks that the solar day (time taken from a sun dial) does not accord with the mean day. This variation is due in part to the earth's eccentric path around the sun and, in part, to the inclination of the earth's axis to the equator. These factors sometimes act in concert and sometimes in opposition which means that whilst mean time is a constant factor, solar time can vary throughout the year by as much as 16 minutes fast or slow of mean time. Clocks showing solar time had been invented by 1700 but they were very simple affairs compared to Berthoud's invention, which required elaborate and highly complicated differential gearing. The result of which meant he was able to display two minute hands revolving in concert on the same dial, with the mean time hand displaying 'regular' time whilst the solar hand is constantly varying in front or behind the mean hand throughout the year.