<P> Christiaan Huygens proved in 1673 that the pivot point and the center of oscillation are interchangeable . This means if any pendulum is turned upside down and swung from a pivot located at its previous center of oscillation, it will have the same period as before and the new center of oscillation will be at the old pivot point . In 1817 Henry Kater used this idea to produce a type of reversible pendulum, now known as a Kater pendulum, for improved measurements of the acceleration due to gravity . </P> <P> One of the earliest known uses of a pendulum was a 1st - century seismometer device of Han Dynasty Chinese scientist Zhang Heng . Its function was to sway and activate one of a series of levers after being disturbed by the tremor of an earthquake far away . Released by a lever, a small ball would fall out of the urn - shaped device into one of eight metal toad's mouths below, at the eight points of the compass, signifying the direction the earthquake was located . </P> <P> Many sources claim that the 10th - century Egyptian astronomer Ibn Yunus used a pendulum for time measurement, but this was an error that originated in 1684 with the British historian Edward Bernard . </P> <P> During the Renaissance, large hand - pumped pendulums were used as sources of power for manual reciprocating machines such as saws, bellows, and pumps . Leonardo da Vinci made many drawings of the motion of pendulums, though without realizing its value for timekeeping . </P>

What is the basic unit of length that a scientist is likely to use