The Salisbury Cathedral clock, built in 1386, is considered to be the world's oldest surviving mechanical clock that strikes the hours.[12] Later developments Clockmakers developed their art in various ways Building smaller clocks was a technical challenge, as was improving accuracy and reliability Clocks could be impressive showpieces to demonstrate skilled craftsmanship, or less expensive, mass-produced items for domestic use The escapement in particular was an important factor affecting the clock's accuracy, so many different mechanisms were tried. Spring-driven clocks appeared during the 15th century,[13][14][15] although they are often erroneously credited to Nürnberg watchmaker Peter Henlein (or Henle, or Hele) around 1511. The earliest existing spring driven clock is the chamber clock given to Peter the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum.[14] Spring power presented clockmakers with a new problem; how to keep the clock movement running at a constant rate as the spring ran down This resulted in the invention of the stackfreed and the fusee in the 15th century, and many other innovations, down to the invention of the modern going barrel in 1760. Early clock dials did not use minutes and seconds A clock with a dial indicating minutes was illustrated in a 1475 manuscript by Paulus Almanus, and some 15th-century clocks in Germany indicated minutes and seconds.[20] An early record of a second hand on a clock dates back to about 1560, on a clock now in the Fremersdorf collection. However, this clock could not have been accurate, and the second hand was probably for indicating that the clock was working. During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nuremberg and Augsburg, and in Blois, France Some of the more basic table clocks have only one time-keeping hand, with the dial between the hour markers being divided into four equal parts making the clocks readable to the nearest 15 minutes Other clocks were exhibitions of craftsmanship and skill, incorporating astronomical indicators and musical movements The cross-beat escapement was invented in 1584 by Jost Bürgi, who also developed the remontoire Bürgi's clocks were a great improvement in accuracy as they were correct to within a minute a day. These clocks helped the 16th-century astronomer Tycho Brahe to observe astronomical events with much greater precision than before. A mechanical weight-driven astronomical clock with a verge-and-foliot escapement, a striking train of gears, an alarm, and a representation of the moon's phases was described by the Ottoman engineer Taqi al-Din in his book, The Brightest Stars for the Construction of Mechanical Clocks (Al-Kawākib al-durriyya fī wadh' al-bankāmat al-dawriyya), published in 1556-1559.[23] Similarly to earlier 15th-century European alarm clocks,[24][25] it was capable of sounding at a specified time, achieved by placing a peg on the dial wheel At the requested time, the peg activated a ringing device The clock had three dials which indicated hours, degrees and minutes He later made an observational clock for the Istanbul observatory of Taqi al-Din (1577–1580), describing it as "a mechanical clock with three dials which show the hours, the minutes, and the seconds." This was an important innovation in 16th-century practical astronomy, as at the start of the century clocks were not accurate enough to be used for astronomical purposes.[26] French rococo bracket clocks, (Museum of Time, Besançon)
