This project, whose website (http://http.hq.eso.org/outreach/spec-prog/aol/market/collaboration/erathostenes/) was last updated in 1996, appears to be hosting 'amateur science'. Eratosthenes was not an amateur, but the equipment available to him made the skills he had on hand harder to use. So everyday laymen have all the tools they need to "re-do" this experiment in finding the circumference of the earth.

By the way, this is one of the 'tell-all' experiments that shows that people really did believe that the earth is round back in the day.

To find the circumference of the earth:

1. Equipment: Two 'tall' poles (40 feet ought to do it...), long-range communications devices (cell-phones, computers with internet connectivity, etc.), syncronized distance-measuring devices, syncronized timekeeping devices, plumbobs or other leveling devices.
2. Teams: there needs to be two of these.
3. Locations: there needs to be two of these as well, and it is best if they are on the same meridian and several hundred miles apart. It is also necessary that both locations have sunshine at the same time.
4. Procedure:
1. Both teams raise their poles and make sure they are gravitationally vertical, steady, and that the top of each is at the same height above ground as the other.
2. At an appointed time when both locations have sunshine (use communications devices to assure this), both teams measure the length of the shadows cast by their respective poles.
3. The teams then share data, and calculate.
5. Calculations: the height (H) of the pole over the shadow length (L) is equal to the tangent of the angle (A) that the ray of sunshine comes though at in that location. So A=arctan(H/L). Subtract one angle from the other to get a difference (D). Multiply the distance (d) from one location to the other times 360/D. So C=d*360/D where C is the circumference of the earth.

Easy, no? At the above website, it mentions that the earth isn't really a globe, it's more of an ellipsoid (longer around the equator than through the poles).