Gradian (gon)
The gradian, also known as gon or grad, was established in France following the French Revolution to promote a decimal-based system of angular measurement. In this system, a circle is divided into 400 gradians, resulting in a right angle measuring exactly 100 gradians. The gradian aimed to make calculations easier by matching the decimal metric system. While it did not gain universal acceptance, it remains in use within certain engineering and surveying practices, especially in France and parts of Central Europe. Its straightforward decimal approach is convenient, but degrees and radians are more widely used globally.
Arc Second (″)
The arc second, symbol ″, is equal to 1/60 of an arc minute or 1/3,600 of a degree, so there are 3,600 arc seconds in one degree and 1,296,000 arc seconds in a full circle. Like the arc minute, it has deep roots in Babylonian astronomy and has remained vital for precision measurement. Arc seconds are heavily used in astronomy to describe angular distances between stars or the apparent size of celestial objects. In geodesy and cartography, arc seconds are used to define coordinates with extreme accuracy. Modern telescopes and space missions often measure distances in arc seconds, reflecting the importance of this unit in advancing scientific discovery.