In Marco's case the geometry is slightly different because he uses an Ortofon SPU which is pre-mounted in its own headshell with no overhang adjustment. Therefore, the arm length is not adjustable and the geometry relies on the arm mounting hole being in a very specific location - I believe it is about 4mm different to that stated by Jelco (which assumes that you have the benefit of a slotted headshell to make fine adjustment).