The verge escapement, being virtually the only one known when the pendulum was introduced, calls for a large pendulum arc, unless gearing is introduced between the escapement and pendulum, or the escapement is very much modified, as in 18th-century Comtoise clocks. Verge-pendulum clocks usually have short pendulums swinging through a large arc. When the anchor escapement was introduced, the smaller pendulum arc enabled much longer pendulums to be used, and led to better timekeeping because of the reduction in circular and escapement errors. This led to the title of 'royal' pendulum being given to the pendulum beating seconds with an effective length of 39. 139921 in.