I just found this and two other old folding rulers and am completely in love with them; I keep carrying them around as they are just a complete delight to hold in the hand, and how much better to measure little things with one of these than with a clunky measuring tape! I am not entirely certain the maker of this one--I have found a "No. 57" (which is how this one is marked)) attributed to E.A. Stearns Co., but also one attributed to Stanley, and I think that is likely correct. I believe late 19th or very early century and for sure a very finely made, beautiful thing, with the numbering on the exterior fairly faded but very bright and clear on the inside, which is the only side one needs. It unfolds to 12 inches via two unfoldings, and two of the original three pins remain in tact to lock it in place when folded up.
12" x 1/4" x 1/8" when completely unfolded; 3 3/8" x 5/8" x 5/16" when completely folded. Very good condition, with a bit of darkening to the boxwood (which is buttery smooth and just gorgeous) of the exterior, minor. I have not touched either the wood or the brass, which is in very condition.