Riefler escapement electric motor every 30 seconds, to eliminate the effect of changes in drive force on the mechanism. Working Riefler precision pendulum clocks on display to the public are located in the lobby of Olin Hall at Carleton College in Northfield, MN, the Deutsches Museum in Munich, the National Watch and Clock Museum in Columbia PA, the Musée international d'horlogerie in La Chaux-de-Fonds and the Musée d'horlogerie in Le Locle (both in Switzerland), the Deutsches Uhrenmuseum in Furtwangen, and at the US Naval Observatory (by appointment only) in Washington DC. Riefler escapement The Riefler escapement is a mechanical escapement for precision
Escapement is made from a special steel alloy with 36% nickel called Invar whose length changes very little with temperature, swings as free of external influence as possible sealed in a vacuum chamber and does no work. It is in mechanical contact with its escapement for only a fraction of a second every 30 seconds. A secondary "slave" pendulum turns a ratchet, which triggers an electromagnet slightly less than every thirty seconds. This electromagnet releases a gravity lever onto the escapement above the master pendulum. A fraction of a second later (but exactly every 30 seconds), the motion of the master