Of course found in Maine, and I know pulled out of an old boat builder's shop in Ellsworth, near Bar Harbor. I know little about the art of boat building, but sure do love a handmade tool, and clearly this was used for marking angles, I presume in a similar way to a bevel gauge. I love it as an object, with to my eye great beauty to all those graphite drawn lines, and I especially love the the knot in the wood on the left edge toward the bottom, simply written/drawn over. Precise but make do, made with care by a CH Closson, who I presume made great use of it. I have found a record of a Charles Henry Closson, 1845-1906 of Sedgwick, Maine, who I believe was the maker. 

17 5/8 x 4 11/16 and in very good condition, with a hole at top for hanging.