Acu-Arc® Adjustable Ruler
The Acu-Arc® adjustable ruler takes over where the ordinary compass leaves off, eliminating the need for numerous beams compasses, and assorted railroad & highway curves. The 12" (30 cm) ruling edge is easily adjusted for drawing curves and arcs. It is made of a rugged plastic material that will not break with normal use. In fact, it can be especially useful in the field when you need to make those last minute changes.
The 12" (30 cm) ruling edge is easily adjusted for drawing curves of any radius from 6.75" to 200" or from 17 cm to 500 cm in the metric model.