Off by about one second. The Sūrya-Siddhānta encodes the Moon's orbit as a ratio of two whole numbers — 57,753,336 revolutions in an Age of 1,577,917,828 days — which works out to a sidereal month of 27.321674 days. The modern measured value is 27.321662. A Sanskrit text whose core is ~fifteen centuries old carries the Moon's period to within 1.1 seconds — a precision Babylonian and Greek lunar theory also reached, each tradition by its own route.