Accurate Mechanical Clocks
Source: National Institute of Standards and Technology Physics Laboratory
In Europe during most of the Middle Ages (roughly 500 to 1500 A.D.), technological advancement was at a virtual standstill. Sundial styles evolved, but not far from ancient principles.
Then, in the early-to-mid-14th century, large mechanical clocks began to appear in the towers of several large Italian cities. These clocks that were weight-driven and regulated by a verge-and-foliot escapement. Like water flow, the rate was difficult to regulate.
Another advance was the invention of spring-powered clocks between 1500 and 1510 by Peter Henlein of Nuremberg. They slowed down as the mainspring unwound.