CALIBER-Rule, is an instrument, wherein a right line is so divided, as that the first part being equal to the diameter of an iron or leaden ball of one pound weight, the other parts are to the first, as the diameters of balls of two, three, four, &c. pounds, are to the diameter of a ball of one pound. The caliper is used by engineers, from the weight of the ball given, to determine its diameter or caliper, or vice versa.