Mechanical Chronometers, a special watch!

The crucial problem was to find a resonator that remained unaffected by the changing conditions met by a ship at sea. The balance wheel harnessed to a spring solved most of the problems associated with the ship's motion. Unfortunately, the elasticity of most balance spring materials changes relative to temperature. To compensate for ever-changing spring strength, the majority of chronometer balances used bi-metallic strips to move small weights toward and away from the center of oscillation, thus altering the period of the balance to match the changing force of the spring. The balance spring problem was solved with a nickel-steel named Elinvar for its invariable elasticity at normal temperatures. The inventor was Charles Edouard Guillaume, who won the Nobel Prize for physics in recognition for his metallurgical work (the only Nobel that has been granted for work related to horology).

The escapement serves two purposes. First, it allows the train to advance fractionally and record the balance's oscillations. At the same time, it supplies minute amounts of energy to counter tiny losses from friction, thus maintaining the equilibrium of the oscillating balance. The escapement is the part that ticks. Since the natural resonance of an oscillating balance serves as the heart of a chronometer, chronometer escapements are designed to interfere with the balance as little as possible. There are many constant force and detached escapement designs, but the most common are the spring detent and pivoted detent. In both of these, a small detent locks the escape wheel and allows the balance to swing completely free of interference except for a brief moment at the center of oscillation, when it is least susceptible to outside influences. At the center of oscillation, a roller on the balance staff momentarily displaces the detent, allowing one tooth of the escape wheel to pass. The escape wheel tooth then imparts its energy on a second roller on the balance staff. Since the escape wheel turns in only one direction, the balance receives impulse in only one direction. On the return oscillation, a passing spring on the tip of the detent allows the unlocking roller on the staff to move by without displacing the detent.

Chronometers often included other innovations to increase their efficiency and precision. Hard stones such as ruby and sapphire were often used as jewel bearings to decrease friction and wear of the pivots and escapement. Until the end of mechanical chronometer production in the third quarter of the 20th century, makers continued to experiment with things like ball bearings and chrome-plated pivots.

Marine chronometers always contain a maintaining power which keeps the chronometer going while it is being wound, and a power reserve to indicate how long the chronometer will continue to run without being wound. Marine chronometers are the most accurate portable mechanical clocks ever made, achieving a precision of around a tenth of a second per day. This is accurate enough to locate a ship's position within 4,600 feet (1,400 m) after a month's sea voyage.

3345, Watches Australia.