The Second was historically calculated as a function of the Earth's rotation. However, it was understood that the earth's rotation was too imprecise and therefore it was decided to measure the second according to the Earth's revolution around the Sun. Over the last three hundred years, the pendulum was the most reliable time. For a pendulum clock to be able to accurately measure time, the range of motion must be kept constant. This is not easy, since frictional losses have an influence on the mechanical system of the watch. Small variations in the amplitude of the pendulum's movement, such as 4° or 5°, make the clock ahead about 15 seconds per day. To compensate for this variation, pendulum clocks use a weights system, which is intended to provide additional energy to the pendulum, and thus compensate for frictional losses. In the last decades, these clocks have almost disappeared, having been replaced by watches with atomic or electronic oscillations, which are much more accurate and reliable than the previous ones.
The Day is a unit of time generally defined as an interval equal to 24 hours. One day, it is understood as the period of time, that the Earth leads to make a rotating movement around itself. Mainly due to the effects of the tides, this period of rotation of the Earth is not constant, resulting in small variations throughout the year. To counteract these small oscillations, in 1955, astronomers defined a new time scale based on the distance from Earth to the Sun, which is more accurate than the rotational motion of our planet. Given that a full rotation is 360º, if we divide this value by the 24 hours that a day has, we will get 15º. So if on a beautiful summer day we are on a beach to catch the sun, for an hour without moving, then without leaving the same place, there was a displacement of our body of 15º in relation to the axis of our planet.