Permanent monuments shall be accurately set and established at the intersections of all outside boundary lines of the plat; at the intersections of those boundary lines with all street lines; at diagonally opposite corners of each street intersection; at the beginning and end of all curves; at points on curves where the radius or direction changes; and at such other points as are necessary to establish definitely all lines of the plat, except those outlining individual lots. In general, permanent monuments shall be placed at all critical points necessary to correctly layout any lot in the subdivision. Monuments shall consist of one-inch iron pins twenty-four inches in length or other approved type of monument. Iron pins three-quarters of an inch in diameter and thirty inches long shall be placed at all corners and all changes in direction of lot lines.