What fraction of the Earthquot;s circumference did Eratosthenes find for the distance between Syene and Alexandria?

What fraction of the Earth"s circumference did Eratosthenes find for the distance between Syene and Alexandria? 1/50 (which he had determined from about a 7 angle of arc) How did he measure the distance between the two cities? He hired a man to pace out the entire distance from Alexandria to Syene. How close was Eratosthenes in his calculation to the correct answer?