Lever escapement

A lever escapement stands between the geared train and the balance. A pivoted lever, the pallet fork, carries two pallets that alternately lock and release the escape wheel, and at each release the lever pushes the balance on through a pin on the balance staff. In the earliest form the escape wheel's "pointed teeth", in the Seiko Museum Ginza's words, "would push against the pallet stones of the anchor". Because the balance is joined to the train only for that brief push and swings free through the rest of its arc, the escapement is called detached.

The invention is attributed to the English watchmaker Thomas Mudge, but the sources do not agree on the year. The Seiko Museum Ginza states: "Around 1756, the English watchmaker Thomas Mudge invented a detached lever escapement (ratchet tooth lever escapement)." The Antiquarian Horological Society (a learned society rather than an issuing authority) dates it earlier, listing under 1754 "Thomas Mudge's Experimental Marine timekeeper, the first example of the detached lever escapement", and separately under 1769 "Thomas Mudge completes his detached lever watch for Queen Charlotte." The Royal Collection Trust's record for that watch says it "incorporates the earliest known example of the lever escapement". This Codex reports the disagreement rather than choosing a year.

The pointed-tooth original was later displaced by the club tooth escapement, whose teeth, in the museum's words, "resembling golf clubs" could "absorb the impulse of the escape wheel with the flat surface".

What this Codex does not do: cite a standard here. The Federation of the Swiss Watch Industry's published list of available NIHS norms contains no norm titled for the escapement, the anchor or the escape wheel. The account above rests on museum and learned-society records, named in the prose.