install and remove them. Large mainsprings in clocks are immobilized by "mainspring clamps" before removal. History Mainsprings appeared in the first spring-powered clocks, in 15th-century Europe. It replaced the weight hanging from a cord wrapped around a pulley, which was the power source used in all previous mechanical clocks. Around 1400 coiled springs began to be used in locks, and many early clockmakers were also locksmiths. Springs were applied to clocks to make them smaller and more portable than previous weight-driven clocks, evolving into the first pocketwatches by 1600. Many sources erroneously credit the invention of the mainspring to the Nuremberg clockmaker Peter Henlein (also spelled Henle, or Hele) around 1511. However, many references in 15th-century sources to portable clocks 'without weights', and at least two surviving examples, show that spring-driven clocks existed by the early years of that century. The oldest surviving clock powered by a mainspring is the Burgunderuhr (Burgundy Clock), an ornate, gilt chamber clock, currently at the Germanisches Nationalmuseum in Nuremberg, whose iconography suggests that it was made around 1430 for Philip the Good, Duke of Burgundy. The first mainsprings were made of steel without tempering or hardening processes. They didn't run very long, and had to be wound twice a day. Henlein was noted for making watches that would run 40 hours between windings. The 18th century methods of making mainsprings are described by Berthoud and Blakey Constant force from a spring A problem throughout the history of spring-driven clocks and watches is that the force (torque) provided by a spring is not constant, but diminishes as the spring unwinds (see graph). However, timepieces have to run at a constant rate in order to keep accurate time. Timekeeping mechanisms are never perfectly isochronous, meaning their rate is affected by changes in the drive force. This was especially true of the primitive verge and foliot type used before the advent of the balance spring in 1657. So early clocks slowed down during their running period as the mainspring ran down, causing inaccurate timekeeping. Two solutions to this problem appeared in the early spring-powered clocks in the 15th century; the stackfreed and the fusee: Stackfreed The stackfreed was an eccentric cam mounted on the mainspring arbor, with a spring-loaded roller that pressed against it. The cam had a 'snail' shape so that early in the running period when the mainspring was pushing strongly, the spring would bear