I marvel at people that can put a square edge on a board by hand planing without jigs or any aids. I have practised this skill for many months and sometimes i get it, most of the time i don't. It seems to me that you must start off at 90 degrees to the face side and rigorously maintain this position to ensure that you finish up with a square edge throughout the entire length of the board. For those that can do this, how do you know you've got the plane sitting at 90 degrees to the face side when you start? How do you keep the plane at this constant angle throughout? By feel, by sight, what cues do you use? I am right-handed and i tend to lean the plane to the left slightly even though it looks perpendicular to the face side to me as i plane. I should also say that i curl 3 fingers on my left hand against the face side as a guide.