My math is a litte rusty, but circumference is diameter x pi()
distance is circumference of the center of the string on the wheel, so it would be a bit more.
1 meter / 7 / pi() = 45.47 cm ( being in the US, I use inches, hope that should be 45 cm not 45mm)
so, the outside diameter of the measuring wheel would be set for exactly 7 rotations to equal 1 meter ?
Once you get this up and running, it would not be hard to calibrate this for a pretty high accuracy of length.
as for the project, Robin2 covered the steps you need to take.