Measuring time involves using various tools and systems to quantify the passage of time. The most common unit of time is the second, which is part of larger units like minutes, hours, days, and years. Clocks and watches are devices that help us keep track of time, while calendars organize days into months and years. Historically, people used natural events, such as the position of the sun or the changing phases of the moon, to measure time. Today, atomic clocks provide the most precise measurements, relying on the vibrations of atoms to define the second. This accuracy is essential for technologies like GPS and telecommunications.