carpenter's rule

He arose, joint by joint, as a carpenter's rule opens, and beat the dust from his clothes.

One was an aged, dignified, stern-looking gentleman, clad as for a solemn festival in grave and costly attire, but with a great bloodstain on his richly wrought band; the second, an aged man, meanly dressed, with a dark and malign countenance, and a broken halter about his neck; the third, a person not so advanced in life as the former two, but beyond the middle age, wearing a coarse woollen tunic and leather breeches, and with a carpenter's rule sticking out of his side pocket.

Jupenet smiled like a man who has an answer for everything; then he pulled out -- still from his pocket -- a little metal ruler, composed of two parts, like a carpenter's rule, against which he put together, and in a line, the characters, holding them under his left thumb.