This rule, made by Hans Christoph Schissler, was used for military purposes (such as determining the calibers of stone and lead projectiles), land surveying, and time reckoning. Accordingly, there are a scale of weights for cannonballs, a linear measurement scale in Roman feet, a small magnetic compass in the leg joint, a viewer at the end of one leg, and a cross-arm with the scale of diurnal hours. A second cross-arm and plumb bob (missing) enabled the instrument to be used as a gunner's level for measuring inclinations and adjusting gun elevation. Brought to Florence from Germany by Prince Mattias de' Medici in the first half of the seventeenth century.