The gnomon is a simple device consisting of a vertical rod or pillar with a horizontal crossbar at the top. The shadow cast by the crossbar indicates the time of day.

A water clock, also known as a clepsydra, works on the principle of the flow of water. Water is allowed to flow from one container to another at a constant rate, and the time is measured by marking the water level at regular intervals.

Hourglass, sandglass, and sand timer are all different names for the same device, which consists of two glass bulbs connected by a narrow neck. Sand is allowed to flow from the upper bulb to the lower bulb at a constant rate, and the time is measured by marking the sand level at regular intervals.

An astrolabe consists of a graduated circle, a pointer, and a sighting tube. The graduated circle is used to measure the altitude of celestial bodies, the pointer is used to indicate the time, and the sighting tube is used to sight celestial bodies.

Varahamihira, a renowned Indian astronomer and mathematician, is credited with the invention of the astrolabe in the 6th century CE.

A sundial is a device that uses the position of the sun to tell the time of day. It consists of a flat surface with a pointer or gnomon that casts a shadow. The position of the shadow indicates the time of day.

A weight-driven clock is a mechanical clock that uses a weight to power its mechanism. The weight is attached to a cord or chain that is wrapped around a drum or pulley. As the weight falls, it turns the drum or pulley, which in turn drives the clock's mechanism.

A gear train is the main component of a weight-driven clock. It consists of a series of gears that transfer the power from the weight to the clock's mechanism. The gear train also regulates the speed of the clock.

Brahmagupta, a renowned Indian astronomer and mathematician, is credited with the invention of the weight-driven clock in the 7th century CE.

A pendulum clock works on the principle of the swinging of a pendulum. The pendulum is a weight suspended from a pivot. As the pendulum swings, it drives the clock's mechanism. The period of oscillation of the pendulum is constant, which makes it a reliable timekeeper.

The pendulum clock was not invented in India. It was invented by Christiaan Huygens, a Dutch scientist, in the 17th century CE.

A mainspring is the main component of a spring-driven clock. It is a coiled spring that stores energy when it is wound up. When the mainspring is released, it unwinds and drives the clock's mechanism.

The spring-driven clock was not invented in India. It was invented by Peter Henlein, a German locksmith, in the 15th century CE.

A quartz crystal is the main component of an electronic clock. It is a piezoelectric material that vibrates at a constant frequency when an electric current is applied to it. This vibration is used to drive the clock's mechanism.

The electronic clock was not invented in India. It was invented by Warren Marrison, a Canadian physicist, in the 20th century CE.