HISTRY OF WATCH
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FIRST WATCH
POKETWATCH
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A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and ever since between Robert Hooke and Christiaan Huygens. Prior to this, the only force limiting the back and forth motion of the balance wheel under the force of the escapement was the wheel's inertia. This caused the wheel's period to be very sensitive to the force of the mainspring. The balance spring made the balance wheel a harmonic oscillator, with a natural 'beat' resistant to disturbances. This increased watches' accuracy enormously, reducing error from perhaps several hours per day to perhaps 10 minutes per day, resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France.[13] The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two century wave of watchmaking innovation.
The first thing to be improved was the escapement. The verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. In Britain a few quality watches went to the duplex escapement, invented by Jean Baptiste Dutertre in 1724. The advantage of these escapements was that they only gave the balance wheel a short push in the middle of its swing, leaving it 'detached' from the escapement to swing back and forth undisturbed during most of its cycle.
During the same period, improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century.
