A friend of mine picked this up at a local swap meet and I don’t think he gave too much for this Brazilian Rosewood 3 beam marking/mortice/tenon gauge. Here is a link to Christian Sholl’s Patent. It is American made and Sholl also patented a 4 beam marking/mortice gauge and some of these are actually made and judging from the prices are quite rare.
I have seen a lot of marking gauges in my time, this one is up there in curious designs. I fiddled with this for a while and it is most difficult to set, the mortice slide adjusts easy enough but getting all three sides in the correct position is a handful.
This view shows the triple beams and the pentagonal shape.
It has several round brass discs on the opposite side of the fence for wear, two are missing. It is brass mounted with iron screws and iron/steel scribing pins.