ABSTRACT
Known also as proportional compasses, they are instruments used to enlarge or reduce drawings, consisting of two crossed arms with sharp points at each end. The arms are held together by a pivot. The position of the pivot determines the ratio of the separation of the points at opposite ends of the instrument. Proportional dividers with a fixed pivot have been known since antiquity; an example survives that was excavated from the ruins of Roman Pompeii.
