A BP A and B represent a section of a line in 3d space. (So a line goes through them.) P is on an imaginary plane, which is perpendicular to the line which goes through on A and B. (So the A-B vector is the normal vector of that imaginary plane.) I need to get an afloat number that represents the range, where the plane intersects this AB section. So if the plane intersects exactly the A point, the result should be 0, if it intersects exactly on the B point, it should be 1. Of course, there are cases when it's less than 0, or more than 1. This float number is the number I need. I need the deduction to put it in my small script, so that would be great if you would insert just a few comments to make me understand the partial results.