To ensure accuracy and precision, it has tapered edges and machine-engraved graduations. 

This brand, (US Blue co. ) is very hard to find, bamboo engineer triangular scale is equipped with graduations including 10, 20, 30, 40, 50, and 60 parts to the inch. It is double numbered. This Antique American made  Bamboo Engineer Triangular Scale is 12 inches in length. It is packed in the original paper/ cardboard type case  See picture.

White plastic over Bamboo.  I know this is an antique because I have owned it for 50+years  - excellent condition, very little use