Surya Siddhanta
एकज्यापक्रमानीतैर् योजनैः परिवर्जिते । भूमिकक्षाचतुर्थाम्शे व्यक्षाच् छेषैस् तु योजनैः॥
Subtract from the fourth part ol the earth's periphery (kaksha) the number of yojanas derived from the declination found by the sine of one sign : at the distance from the place of no latitude of the remaining number of yojanas.
english translation