"These are similar to 2-fold and 4-fold "carpenters" rules sometimes referred to as 2-foot rules. There were variations used in tailoring and other trades from the later 19th and early 20th century. Wooden 4-foot rules are still made although not of the same quality materials (and certainly not ivory as some of the small models were). Also can be used for several geometry tasks when operated as a "sector". "

"https://en.wikipedia.org/wiki/Cone_of_Silence_(Get_Smart)"