Eratosthenes' measuring (ET- cameo)

Juan Luis Salguero Rodríguez, Etwinning Prize 2010, shows us a piece of his wonderful work "Maths and Earth", related (what else?) with classical world: Measuring and calculating Earth's circumference.

Is it possible to calculate Earth radius 200 years B.C.? Yes! It was done by Greek mathematician, geographer and astronomer:
Eratosthenes. We decided to repeat the experience made over 2000 years ago.
We were inspired by Spanish teacher who looked for partners to such measuring on the first day of spring, 20th March.
You can see this project clicking here.