An ingenious curve drawing tool, create or measure both small and large curves. Great for drafting & woodworking two versions available: the inch ruler use to measure & draw curves with radii between 7” to 200” & the metric ruler use to measure & draw 17cm to 500cm. It is simple to use. To measure an existing curve loosen knob, bend ruler edge to conform to curve, and read the radius off the ruler. For Scaled drawing set Acu-Arc to scale of drawing or use to find center line of arc, tighten and draw. Note that the working edge of the ruler is about 12”.