The vernier caliper , invented by the French scientist Pierre Vernier(1580-1637), is a well-known tool for high-resolution length measurements . The caliper consists of two graduated scales , a main scale like a ruler and a second scale , the vernier , which slides parallel to the main scale . The two scales have a small relative prich difference, e.g. 1/20. In other words , any change in position is enhanced by a factor equal to the inverse of the relative pitch difference.