YBC 7289 is a Babylonian clay tablet notable for containing an accurate sexagesimal approximation to the square root of 2, the length of the diagonal of a unit square. This number is given to the equivalent of six decimal digits, "the greatest known computational accuracy ... in the ancient world".[1] The tablet is believed to be the work of a student in southern Mesopotamia from some time between 1800 and 1600 BC.