*Roller Scale- Roll N Draw Ruller (30cm) and Plastic Triangular Scale/Ruler (30cm) 12 Inch long. Rolling Ruler Rolling is a drawing tool for making parallel lines, hatching etc. Triangular Scale - triangle scale is a simple polygon because no side or angle has the same size, unlike an isosceles foot and an equilateral triangle. Because all sides and angles have different measurements, this triangle is considered an irregular convex polygon.