 He noted, however, that Hipparchus had added some 26,000 stadia to Eratosthenes's estimate.The smaller value offered by Strabo and the different lengths of Greek and Roman stadia have created a persistent confusion around Posidonius's result.Ptolemy used Posidonius's lower value of 180,000 stades (about 33% too low) for the Earth's circumference in his "Geography".