Circa 1920-50s American Optical Co. (Keuffel & Esser) 6-Inch (15 cm) Boxwood Ruler

A very handy 6 inch (15 cm) ruler that probably dates from the 1920s to 50s. Sold by the American Optical Company (founded 1833, incorporated 1869), it was most likely manufactured by Keuffel & Esser. It is solid boxwood with "Ivorite" (ABS plastic), with 16th graduations on one side, and millimeter graduations on the other.