A traditional mechanical pendulum clock loses approximately 0.5 seconds every day due to air resistance and friction at its pivot points.

Mechanical pendulum clocks keep time through the harmonic motion of a swinging weight. Galileo Galilei first scientifically studied this principle in 1582, and Christiaan Huygens refined it further in 1656, creating the first practical pendulum clock. Despite careful engineering, these clocks remain vulnerable to atmospheric drag and mechanical friction at the suspension point.Air resistance acts directly against the pendulum's motion, while friction at the pivot converts kinetic energy into heat. Even exceptional timepieces, such as those crafted by John Harrison in the 18th century, lost a fraction of a second daily. These forces reduce the amplitude of each swing, which can subtly lengthen the period of oscillation.The Shortt-Synchronome clock, developed in 1921, represented a major breakthrough. It used two pendulums—one suspended in a vacuum chamber to eliminate air resistance—and achieved accuracy within 0.01 seconds per day. Even this impressive feat is dwarfed by modern atomic clocks. The NIST-F2 cesium atomic clock at the National Institute of Standards and Technology, for example, maintains accuracy to within one second every 300 million years.