Trixie raised her hand. "Do you mean how he can't be exactly right?" she asked. "Well for a start Syene isn't exactly on the Tropic of Cancer, but slightly North, and he used this in order to make his measurements. And as I mentioned just a minute ago, Alexandria isn't exactly south of Syene. The last is that the sun appears as a disk located at a finite distance from the earth instead of as a point source of light at an infinite distance" she siad sounding like a ravenclaw. Woah. "So therefore the distances weren't exactly reliable" she smiled. "But giving him credit, his measurements were extremely close to the actual measurements. Which as you said was pretty impressive for a guy of his era" she giggled.