Additional functions in clocks besides basic timekeeping are called complications. The study of timekeeping is known as horology. Bees have an internal clock with three different synchronization or timekeeping mechanisms. PPS signals are used for precise timekeeping and time measurement. He invented the pendulum clock, which was a major step forward towards exact timekeeping. For serious precision timekeeping, a more specialized GPS device is needed. Sundials had been used for timekeeping since ancient Egypt. These devices functioned as timekeeping devices and also as calendars. In the 18th and 19th century escapement design was at the forefront of timekeeping advances. This property, called isochronism, is the reason pendulums are so useful for timekeeping. Much of early Chinese astronomy was for the purpose of timekeeping. Calendars are explicit schemes used for timekeeping. It was a complex device that was about high, and had multiple functions alongside timekeeping. This was also the first example of the Olympics exclusively using electronic timekeeping equipment . In Vedic timekeeping, a tithi is a lunar day.