Pierre Le Roy, the eldest son of Julien Le Roy, as important or more important than his father, was the teacher of Ferdinand Berthou, who would later become his fiercest competitor. He created the "theory of precision" that remarkably outperformed Harrison's H-4, in 1760 he applied the "Stackfreed" or regressive brake, the balance for temperature change and the isochronous spiral, among other discoveries. For years, he continued to sign his workshop's watches under the name Julien Le Roy as a tribute to his father. He was the horloger de chambre of Louis XVI.
Illustration: silver Pocket watch with smooth case for the Turkish market signed Julien Le Roy in Paris, and made by his son Pierre. The dial features an eye-catching gold center enamel, with the signature of the prestigious watchmaker clearly visible. This type of watch, like Prior's multi-case watches, and those with dramatic and striking enamels, were commissioned in Switzerland by Turkish watchmakers.
