Machine finished from first quality 0.060" clear acrylic. From 0°15" to 20,000" radius, maximum curve length is 18" and width is 1½". Imprinted with the arc in degrees and minutes, the scale, and the radius in hundredths of an inch. Radial line imprinted to indicate the exact point of tangency. Scale is 1" = 100’. Guaranteed to be within ±.010" of the true arc. Packaged in an attractive hardwood case with label identification.