mechanical+construction
131military technology — Introduction range of weapons, equipment, structures, and vehicles used specifically for the purpose of fighting. It includes the knowledge required to construct such technology, to employ it in combat, and to repair and replenish it.… …
132History of timekeeping devices — For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to approximately 2000 BC, in Sumer. The Ancient Egyptians divided the day into two 12 hour periods, and… …
