In Indian astronomy, the prime meridian is the great circle of the Earth passing through the north and south poles, Ujjayini and La?ka, where La?ka was assumed to be on the Earth's equator.
The development of Indian trigonometry, based on sine as against chord of the Greeks, a necessity for astronomical calculations with his own concise notation which expresses the full sine table in just one couplet for easy remembrance. One of the two methods suggested by him for the sine table is based on the property that the second order sine differences were proportional to sines themselves.
In geometry his greatest achievement was an accurate value of ?.