I often use knotty pine and have more than once misjudged the position of a knot on the reverse side of the board and had to start over. The knot finder is easy to use: trace the shape of the knot on one side of the board with the stylus. While you are doing this, maintain light pressure on the arm with the pencil on the opposite side. You’ll end up with the exact shape and position of the knot drawn on the board.
– Richard Ayer