Of all our traditional parallel rules, the Weems & Plath 15-inch (381mm) 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.Features15-inches (381mm) longBrushed aluminum armsPolished aluminum handleMilled acrylic with beveled edgesIncludes protractor scaleProtective plastic sleeve