Before there were calculators, slide rules were the most common tool for quickly finding the answers to simple math problems. In watches, however, this process has gone in reverse. Decades after the advent of digital calculator watches, the Caliper Slide Rule Watch brings the classic mathematical tool to your wrist. By turning the lower crown, you move the interior ring of the rule, which wraps around a semi-transparent face through which the Miyota movement is visible. The case is made from PVD-coated 316L steel, and has a list of handy conversion factors on the reverse side. Available in two styles, it's water resistant to 100 meters.