### Theory:

Clocks are used to measure time intervals.

Type of clock:

• Based on display.
• Based on work mechanism.
Based on display:
• Analog clock.
• Digital clock.
Analog clock: is a traditional or classical clock. It has three hands (for an hour, minute, second) to show the time.
• Hours Hand: Hour hand is used to show the 'hour' using the short and thick.
• Minutes Hand: Minute hand is used to show the 'minute' using the long and thin.
• Seconds Hand: Second hand is used to show the 'seconds' using the long and very thin. And also it makes one rotation in one minute and $$60$$ rotations in one hour
• Analog clocks can be driven either mechanically or electronically.
Digital clock: shows the time directly. It displays the time in numerals and also the symbols. It have both the $$12$$ hours or $$24$$ hours display screen.

Nowadays, digital clocks are showing Date, Day, Month, Year, Temperature, etc.

Digital clocks are also known as Electronic Clocks. Digital clock are used in Railway station, airport, hotels, bank, etc.

Based on work mechanism:
• Quartz clock
• Atomic clock
Quartz clock: is controlled or regulated by 'quartz crystal' (silicon dioxide), which are activated by ‘electronic oscillations’.
• Crystal oscillator creates a signal with a very precise frequency.
• So that the quartz clocks are at least an order of magnitude more accurate than mechanical clocks.
• The first quartz clock was built in $$1927$$ by Warren Marrison and J.W. Horton at Bell Telephone Laboratories.
• The accuracy of one second in every ${10}^{9}$ seconds.

Atomic clock: is making the use of periodic vibrations occurring within the atom.
• The accuracy of one second in every ${10}^{13}$ seconds.
• They are used in tracking navigation systems such as GPS Device (Global Positioning System), GLONASS (Global Navigation Satellite System), and also used by International time distribution services.