I know approximatively how much rake there was on the original fork but i just don't know how to calculate it. Am i suppose to mesure the angle or the distance between the point on the ground where a headtube prolongation would arrive and the point right under the fork end.

**** that last one was hard to explain.

Because the original fork was a 27'' with a 27'' wheel front and back, but now I have switched to 700s.
Switching to a 700 fork will change everythng so I guess that since the headtube is a little more close to vertical the rake of the original fork wont't be the best for my 700 fork.