He was distinguished principally in his mastery and improvement of the clock and chronograph, above all of the marine chronometer, in which he carried forward the pioneering work of John Harrison.

[4] His technique for temperature compensation was highly efficient in that it worked without changing the length of the spiral balance spring, which he had discovered to be isochronous only at a precise given length (i.e. when frequency is independent of amplitude, so that a mechanical clock or watch runs at the same rate regardless of changes in its drive force, so it keeps correct time as the mainspring unwinds).

[4] In 1769, after his chronometre underwent testing aboard the corvette Aurore, he was awarded the double prize offered by the Académie française for the best method of measuring time at sea.

He succeeded in giving his instruments the greatest possible regularity by the discovery of the isochronous spiral spring, in which he was in competition with Ferdinand Berthoud, but which he published first.

[4] The work of Le Roy was not fully recognized in France however, and his contemporary Ferdinand Berthoud became more famous, obtaining the prestigious title of Horloger de Marine, which left Le Roy disillusioned and led him to retire.