RARE BOXWOOD & BRASS 'ONION MAKER' TABLED 2 FT 4 FOLD RULE

Very interesting rule made by ONION. It is name I know but cannot find a reference to in order to date. I am sure this is very early ca 1820-1840 based on the stampings and the 'ONION MAKER' mark. The rule with slide is in very very nice gently warn condition for its age but oddly doesn't open up. It seems like the edges are bound together but likely not difficult to work open.