The Panchanga Yantra is primarily used for calculating the positions of celestial bodies, such as the Sun, Moon, and planets, and for determining the auspicious times for various activities, such as weddings, festivals, and business ventures.

The Panchanga Yantra is based on the Earth's rotation around the Sun and the Moon's orbit around the Earth. These motions cause the positions of celestial bodies to change over time, and the Panchanga Yantra is used to calculate these changes.

The Panchanga Yantra consists of a circular plate with a grid of lines, a pointer that indicates the position of the Sun, and a set of movable disks that represent the positions of the planets.

The Panchanga Yantra is used to calculate the positions of celestial bodies by measuring the angles between the celestial bodies and the horizon, by measuring the time it takes for the celestial bodies to rise and set, and by using trigonometry to calculate the positions of the celestial bodies.

The Panchanga Yantra is used to determine the auspicious times for various activities by consulting the positions of the celestial bodies, considering the day of the week and the time of day, and taking into account the lunar phase.

The Panchanga Yantra has several limitations, including the fact that it can only be used to calculate the positions of celestial bodies that are visible from Earth, it is not accurate enough to be used for scientific purposes, and it is difficult to use and requires a deep understanding of astronomy and mathematics.

The Panchanga Yantra is still used today because it is a traditional instrument that has been used for centuries, it is still accurate enough for many practical purposes, and it is relatively easy to use once you understand the basics.

The Panchanga Yantra has a number of modern applications, including being used to calculate the positions of celestial bodies for astrological purposes, to determine the auspicious times for various activities, such as weddings and festivals, and to teach astronomy and mathematics to students.

The Panchanga Yantra faces a number of challenges in the future, including the increasing popularity of Western astrology, the decline of traditional Indian culture, and the lack of interest in astronomy and mathematics among young people.

There are a number of things that can be done to ensure the continued survival of the Panchanga Yantra, including promoting the teaching of astronomy and mathematics in schools, encouraging the use of the Panchanga Yantra for astrological and other traditional purposes, and developing new and innovative ways to use the Panchanga Yantra.