The big idea
A watch stores energy in a coiled spring and lets it out in tiny, equal pieces. The mainspring gives the push, the balance wheel and its hairspring set the beat, the escapement lets the wheels move half a tooth at a time, and the gears count the beats into seconds, minutes and hours.
Memory trick: “Spring pushes, wheels count, the lever lets them out; the balance keeps the beat, so the time comes out.”
A bit of history: In 1511 the scholar Johannes Cochlaeus praised a Nuremberg craftsman, Peter Henlein, for small spring-driven clocks that could be carried in a purse and ran for 40 hours. In 1675 the Dutch scientist Christiaan Huygens published a design for a spiral balance spring; the English scientist Robert Hooke said he had the idea first. In the 1750s the English watchmaker Thomas Mudge invented the lever escapement, and his first lever watch, finished about 1770 for Queen Charlotte, is still in the Royal Collection.