This page contains the original documentation that came with my Buren Calibre 82 wristwatch, along with English translations of the original German text.
An Extraordinary Work
BUREN “Calibre 82”
In 1970, Buren Watch developed a groundbreaking automatic movement with increased frequency of the balance wheel and two barrels. This “Calibre 82” brought together the best mechanical watch technology available at that time. It is not only a watch movement but also a piece of the history of the development of the mechanical clock.
In the long history of mechanical watches, special attention of watch designers is paid to the development of movements with reliable and accurate time indication.
It was always recognized that “constant force” is the most important condition for achieving a better quality movement.
Only with the battery-powered quartz watch could optimum accuracy be achieved. Even the previously-developed electrically-driven balance wheel was no comparison with quartz movements. Only so-called audio-frequency transducers achieved better results than the electrically driven balance.
Constant force can be difficult to implement in a watch with a spring mechanism due to the ever decreasing force of the spring. Here are just a few of the numerous attempts in this direction:
- Movement with lockable automatic winding and power reserve display from the center, Felsa 11.5”’ 1565
- Movement with automatic winding and two barrels, Buren Watch 11.5”’ 82
- Movement with automatic winding and two barrels, Longines E 12”’
- Movement with two barrels, Favre-Leuba 11.5”’ 253
The “CaIibre 82” of BUREN is superior to the other calibers in various respects. Along with a high frequency of oscillation in the balance wheel, it has a largely constant spring force, and has a very low loss of torque.
The key features of “Calibre 82” can be summarized as follows:
- Optimal frequency of the balance wheel with 36,000 semi-vibrations per hour
- Two smaller springs were chosen in place of a large spring
The very simple design of the gear train prevents “floating” of the seconds hand. Automatic winding of both barrels takes place on both sides using a rotating mass. The drive of the rotor and the teeth of the two coupling rotary parts are arranged in series, so that as little force as possible is lost.
To achieve hand / time setting accurate to the second, a locking mechanism is installed for the second hand. The lock acts on the rim of the balance wheel, pausing vibration when it is engaged.
The chronometric peculiarities of the Buren “Caiibre 82” were measured in 1970 according to the method developed by P. Chopard. This gave a value of 44, which corresponds to a total efficiency of the “Calibre 82” with two barrels of 28%. This is the best result achieved by a mechanical clock by far in a study by this method.
The loss of the spring force after 24 hours was only 13%, while its performance is at least 86%. That is, the long thin spring has an efficiency of 86% and loses only 13% of its torque in 24 hours.
The power output of the barrel teeth for bearing of the balance is 74%. Thanks to the indirect drive of the minutes hand, amplitude fluctuations were significantly reduced to between 5% and 8%.
Although it is difficult, based on relatively few experimental works, to establish a definitive result, the calculated diagram (Fig. 2) clearly shows the differences between the experiments tested, and these are close to the production mechanism. Clearly visible are the exceptionally small fluctuations of ± 60 seconds within 30 days as the maximum deviation, with a minimum of only + 25 seconds. This result is unique in a mechanical wristwatch movement that can be comfortably worn.
Because of its precision, rugged construction, simple upkeep, and uncomplicated gear regulation, “Calibre 82” is referred to in professional circles as the most serious competitor of electronic watches with audio-frequency oscillators.
Buren “Calibre 82” is a pioneering achievement and has written the history of watchmaking by the design of its structure, with the refined combination of two barrels, the simple and extremely energy-saving gear train, and because of its high frequency of 36,000 semi-oscillations per hour.
Hans Kocher, Büren an der Aare
Hans Kocher was chief designer and technical director of the Buren manufacture. He is one of the most well-known Swiss watch engineers and has made a great contribution to the development of automatic movements.