Of all our traditional parallel rules, the 15-inch (38.1cm) Brushed Aluminum Arm Parallel Rule is a best-seller. This sturdy acrylic parallel rule includes a protractor scale, is easy to use, and is a necessary tool for every seagoing navigator. The two straight-edged rules are connected to maintain the same angle. By walking the rules across the chart and securely holding down the non-moving rule, you can effectively plot a course. 15-inches (38.1cm) long Brushed aluminum arms Polished aluminum handle Milled acrylic with beveled edges Includes protractor scale Protective plastic sleeve Lifetime warranty