Hayanaratna 8.51

Now, take the planet born of the true savana (sunrise-to-sunrise) day count. The mean Sun is near the horizon at Lanka, the city of the ten-headed one. As the Siddhanta says, the planet is then the mean one. It is born at the mean Sun's rising time at Lanka. But what is wanted is at the true Sun's rising time. So by the bhujantara (time correction for the Sun's uneven motion) correction it becomes the one at the true Sun's rising time. Again, there is the south-north gap, called the charantara (day-length correction) correction. By it, the planet becomes the one at the rising time in a city on the central line. That city has the same latitude as one's own. Again, there is the east-west gap, called the dashantara correction. By it, the planet becomes the one at the true Sun's rising time in one's own city. This is the truth.

Simple meaning: Why the three corrections: they move the planet from the mean Sun's rising at Lanka to the true Sun's rising at your own city.