Sometimes an old tool just strikes as especially lovely, as was the case with this antique brass watchmaker's double caliper. What do I know about watchmaking? Nothing. But I find the delicacy of this, with its thin, tapering arms, and its symmetry, and the way the sides open and close together very satisfying. Feels like a metaphor for/embodiment of balance and precision!  This would have be used for measuring, truing, and modifying tiny watch components, and the dot one on side and incised notch on the other are I believe alignment marks. I believe it is a copper round at center, held with what looks like a hand-forged steel pin. 

 3" x 1 3/8". Good condition, though I can't testify to precision for use, with a lovely wam patina to the brass and nice general surface wear from handling and use. Later 19th/early 20th century I believe, unmarked.