Galieo's Geometic and Military Compass is a device that was, in some ways, a precursor to the slide rules used in by 20th century engineers. While other individuals such as Fabrizio Mordente and Thomas Hood created similar devices (all called "Sectors"), Galileo's is the best known, perhaps because of his fame in other areas.
Sectors were used by military officers and engineers for a variety of purposes: to measure distances and angles, to make a wide range of mathematical calculations, and even to determine how much gunpowder should be used for a cannonball of a particular type.
Late 1500s to late 1800s
- Galileo's Compass - History of an Invention from the Museo Galileo. Includes a brief history of the device and multiple images.
- Galileo's Instruments of Discovery at the Smithsonian. Includes photos of Galileo's other works.
- A page on The Sector at the Galileo Project.
- Galileo's own book on the operation of his compass, from the Internet Archive. Still in the original Italian.