For example, a pendulum clock moved from sea level to will lose 16 seconds per day. With the most accurate pendulum clocks, even moving the clock to the top of a tall building would cause it to lose measurable time due to lower gravity. Also called torsion-spring pendulum, this is a wheel-like mass (most often four spheres on cross spokes) suspended from a vertical strip (ribbon) of spring steel, used as the regulating mechanism in torsion pendulum clocks. Rotation of the mass winds and unwinds the suspension spring, with the energy impulse applied to the top of the spring. With a period of 12—15 seconds, compared to the gravity swing pendulum's period of 0.5—2s, it is possible to make clocks that need to be wound only every 30 days, or even only once a year or more. This type is independent of the local force of gravity but is more affected by temperature changes than an uncompensated gravity-swing pendulum. A clock requiring only annual winding is sometimes called a "400-Day clock" or "anniversary clock", the latter sometimes given as a wedding memorialisation gift. German firms Schatz and Kieninger & Obergfell (known as "Kundo", from "K und O"), were the main manufacturers of this type of clock. The "perpetual motion" clock, called the Atmos because its mechanism was kept wound by changes in atmospheric temperature, also makes use of a torsion pendulum. In this case the oscillation cycle takes a full 60 seconds. The escapement is a mechanical linkage that converts the force from the clock's wheel train into impulses that keep the pendulum swinging back and forth. It is the part that makes the "ticking" sound in a working pendulum clock. Most escapements consist of a wheel with pointed teeth called the "escape wheel" which is turned by the clock's wheel train, and surfaces the teeth push against, called "pallets". During most of the pendulum's swing the wheel is prevented from turning because a tooth is resting against one of the pallets; this is called the "locked" state. Each swing of the pendulum a pallet releases a tooth of the escape wheel. The wheel rotates forward a fixed amount until a tooth catches on the other pallet. These releases allow the clock's wheel train to advance a fixed amount with each swing, moving the hands forward at a constant rate, controlled by the pendulum.