The Clepsydra (pronounced “clep-see-drah”), more commonly referred to as the “water clock”, was among the earliest technological devices engineered for measuring time, predating mechanical clocks by over a millennia. The earliest known example of a clepsydra is from Ancient Egypt, constructed close to 1400 B.C., and attributed to an Egyptian court official named “Amenemhet” (pronounced “ah-men-ehm-het”). Clepsydra clocks operated using 1 of 2 primary designs; which includes both outflow and inflow setups. In an outflow clepsydra, water exited the chamber container through a small hole at the bottom, and the measurement of time was tracked by the continually lowered water level which was measured against internal markings. Inflow clepsydras reversed this design setup with water entering a marked container vessel, and the continually rising water level indicating the amount of time which had elapsed. The main challenge of the inflow and outflow designs was maintaining a consistent flow rate of water because as water drained, pressure dropped which slowed the drip rate and skewed the clocks accuracy. Ancient Greek engineer Ctesibius (pronounced “teh-sib-ee-us”) addressed this problem by introducing an overflow tank with a fixed water level, ensuring constant pressure and uniform water flow at all times. Ctesibius also added a float regulated valve system, an early feedback mechanism designed to stabilize inflow of water and prevent overflow, much the same as the float controlled fill valve (e.g. ballcock, float cup valve, diaphragm type inlet valve etc.) installed within toilets during the modern day. Subsequent future cepsydra designs implemented gears and escape mechanisms to convert water movement into mechanical energy/motion. Chinese engineers expanded further upon the concept of the clepsydra by introducing polyvascular systems, in which water flowed through multiple containment vessels in an effort to better regulate timing intervals. These innovations permitted water clocks to function independently of sunlight unlike sundials, the prevailing time keeping technology throughout history, and laid the foundation for regulated mechanical timekeeping which proceeded it. Despite limitations (e.g. temperature dependent viscosity, leakage and evaporation, the need for constant manual maintenance by human beings etc.), clepsydras remained in use for centuries and were the first controlled, replicable timekeeping systems in history only falling out of fashion during the late Middle Ages due to the ascendency of mechanical, pendulum and gear based clocks