Duplex

The term duplex generally describes any double system or one that operates in two stages. In watchmaking, it mainly refers to the Duplex escapement, a type ofEscapement with frictional rest invented around 1700 by Robert Hooke, improved by Jean-Baptiste Dutertre and Pierre Le Roy, then finally perfected by Thomas Tyrer, who patented it in 1782. Its originality lies in its Escape wheel fitted with two rows of teeth — hence its name: long locking teeth arranged around the circumference and short impulse teeth standing axially on the plane of the wheel. The Balance receives an impulse on only one of the two Vibrations of each Period, with the other Vibration remaining what is called dead. Very fashionable from 1790 to 1860 in high-quality English pocket watches, it was also used extensively in cheap American watches of the Waterbury type (1880-1898) and enjoyed particular success in watches intended for the Chinese market, where its accuracy, comparable to that of a Detent escapement, was appreciated. Fragile and sensitive to shocks — a violent shock, by stopping the Balance at the wrong moment, prevents it from restarting — it was gradually replaced by the Pallets (lever) escapement, which was more robust. It remains an important milestone in the history of chronometry.