Julien Le Roy (1686-1759) was born in Tours and by the age of thirteen had already made his first clock. By the age of seventeen he was established as apprentice to Le Bon in Paris, where he was so quick and adept at his work that he made and finished a repeating watch in just eight days. Shortly after he had attained his Mastership he was given the Directorship of the French Société des Arts. In 1739 he was appointment Horloger Ordinaire du Roi in 1739. His inventions included turret clocks, equation clocks and pull repeat mechanisms. An innovative clockmaker, he worked closely with the two finest French instrument-makers of the time, Lemaire and Langlois.
The mechanical minute dial solves the problem that most portable sundials cannot achieve an accuracy of better than a quarter of an hour. By using a sighting device rather than a gnomon, a geared mechanism can amplify the movements of the alidade so that a pointer can give the minute of the day. A sundial with a high level of accuracy such as this would have often been used to set a clock or watch to local solar time. A clock can keep the time, of course, but not find it; so the use of an accurate sundial is required.