Acu-Arc Adjustable Ruler
The spring tensioned bar of this 12" "bend-able" rule can be easily adjusted to draw curves of any radius - from 6-3/4" up to a staggering 200". Sliding adjustment knob locks and holds settings. Determine the radius of existing curves for dimensioning drawings; find center lines and center points of curves; and determine at what radius a curve must be "fair" at a particular point or line on a drawing. USA