In present times, various instruments and technologies are used for time measurement. Here are some commonly used ones:
Atomic Clocks: Atomic clocks are the most accurate timekeeping devices available today. They use the vibrations of atoms (typically cesium or rubidium) to measure time. The International System of Units (SI) defines one second as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the cesium atom.
Quartz Clocks: Quartz clocks use a quartz crystal oscillator to measure time. Quartz crystals have a property called piezoelectricity, which means they vibrate at a precise frequency when an electric current is applied. These vibrations are used to generate a stable time base.
GPS Time: The Global Positioning System (GPS) relies on a network of satellites to provide accurate time information. GPS receivers can use the signals from multiple satellites to determine the user's position and also provide highly accurate time synchronization.
NTP and PTP: Network Time Protocol (NTP) and Precision Time Protocol (PTP) are network-based protocols used to synchronize clocks across computer networks. NTP is commonly used for less critical applications, while PTP is used in scenarios where extremely accurate time synchronization is required, such as in financial trading or industrial automation.
Quartz Watches: Quartz watches use a small quartz crystal oscillator to measure time. The crystal oscillates at a fixed frequency, which is divided down to provide the seconds, minutes, and hours.
Digital Clocks: Digital clocks typically use electronic circuits, such as counters and oscillators, to measure and display time. They often rely on a crystal oscillator for stability.
Sundials: While less precise than the aforementioned instruments, sundials have been used for centuries to measure time based on the position of the sun. They consist of a flat plate with a raised dial and a gnomon (a vertical rod that casts a shadow). The position of the shadow can indicate the time.
These are just a few examples of the instruments used for time measurement in present times. Advances in technology continue to improve our ability to measure time with increasing accuracy and precision.