I don't know how much clearer I can say it. I have stated more than once that the movement is back and forth. I am not talking about rod side clearance where the rods slide from front to back on the crank. I am talking about moving the rod towards one side of the block to the other, which is perpendicular to the crank, not parallel, which would be side to side movement.
Maybe you should have included this !
Parallel lines have the same slope and will never intersect. Parallel lines continue, literally, forever without touching (assuming that these lines are on the same plane). On the other hand, the slope of perpendicular lines are the negative reciprocals of each other, and a pair of these lines intersects at 90 degrees.
