Bulova

At that time, accurate clocks had already been built for many years. Said to have been the original idea of Galileo Galilei in 1582, but first built in practice by Christiaan Huygens, in 1656, pendulum clocks could already keep time to within a tenth of a second a day. With the advent of the mainspring, to replace the weights that had traditionally powered these early pendulum clocks, Huygens also invented the spiral balance spring, still found in mechanical clocks and watches to this day. Like the swing of a pendulum, the coiling and uncoiling of this spiral balance spring had a natural periodicity that regulated the unwinding of the mainspring. This new mechanism was able to replace the pendulum and make the clock more compact and portable. By 1761, John Harrison, a self-taught clock maker, had produced a self-contained spring and balance wheel marine chronometer, fully portable and accurate to within a fifth of a second per day.