Need help, does anyone know what this is?

Picked this up at a sale, but I have no idea what it is. All brass body, thumb wheel is also brass, blade is flat steel like a screwdriver, not sharp. Blade does not retract all the way, nor does it come out flush with legs. As you can see by the dollar bill it about 2X3" about 1\2-3\4 " thick. Any help would be greatly appreciated.