I have a vintage 36" wood folding ruler.  It is folds in 3 marked Made in the USA".  It reads "Miller Corrugated Box Co. 289 Kilvert St Warwick RI Tel (401 739-7020".  Overall it is in nice condition with minimal wear showing.  I would estimate that this dates between the 1970's - 1990's.  It is 1 sided showing some light wear

Folding Ruler 36" Vintage