Not sure I totally understand the Kapex and the issue about angles. I followed Peter Parfitt 's video which follows elementary math and few algebra property. So assuming that Side A is straight, assuming that my dogs are perfectly aligned and perpendicular to the rail, here what should happen. I cut side B perpendicular to side A. Turn 90 degree, cut side C perpendicular to side B, same for D perpendicular to C. If everything goes well, I am done because of Math Transitive Law: D is perpendicular to A. Although, I cut side A again to find if there is any difference between the two ends of the cut. After 2 additional attempts, I think that there were 2 issues. My position while cutting and the standard clamps (no Festool) that might have shifted the board. I am getting closer to better results but not as good as Peter. Using a bad ply. Probably if I try with BB, would be best. Anyway, here my result on the "recut" of side A: the difference between the 2 ends is 0.79mm. 0.79mm divided by 369mm (length of the last cut) and divided by 4 gives me 0.00053777. Which is the margin of error on a single cut ( per Peter's video). I think it is ok after all. Correct?