of the escape wheel teeth instead, eliminating complicated adjustments. The pins are located symmetrically on the lever, making beat adjustment simpler. Watches that used these escapements were called pin lever watches, and have been superseded by cheap quartz watches. Future directions One recent trend in escapement design is the use of new materials, many borrowed from the semiconductor fabrication industry. A problem with the lever escapement is friction. The escape wheel tooth slides along the face of the pallet, causing friction, so the pallets and teeth must be lubricated. The oil eventually thickens, causing inaccuracy, and requiring cleaning and reoiling of the movement about every 4 years. A solution is to make the escape wheel and other parts out of harder materials than steel, eliminating the need for lubrication. Materials being tried include silicon, nickel phosphorus, diamond, and diamond-on-silicon. Ulysse Nardin in 2001, Patek Philippe in 2005, and Zenith in 2013 introduced watches with silicon escape wheels. See also Anchor escapement Co-axial escapement References External links An Analysis of the Lever Escapement, by H. R. Playtner, 1910, from Project Gutenberg Escapements