Throughout the Renaissance, many attempts were made to develop a universal instrument that could be used to perform arithmetical calculation and geometric operations easily. This need was felt especially in the military field, where the technology of firearms called for increasingly precise mathematical knowledge. To satisfy these requisites, the first proportional compasses were developed in the second half of the sixteenth century. The geometric and military compass of Galileo (1564-1642), invented in Padua in 1597, belonged to this class of instruments.
The application traces the fortune of the instrument and compares it with other types of coeval compasses. A series of interactive animations allow us to discover the multiple uses of the compass deriving from the possibility of finding with it quantities proportional to assigned quantities, whether they be lines, areas or volumes.