skyeriding
900
There are two types of Lange Balance Cocks - for regulators, and for freesprung balance wheels
Sep 08, 2019,14:22 PM
Before getting into it, let's revisit some theory first to better appreciate the subtleties of why the engraving differences arise.
The 1st gen Lange Chrono uses a regulator to adjust the timekeeping (beat rate). Notice the swan-neck with its screw - it pins a long needle, which is the regulator lever. The regulator is used to control the position of the regulator pins, which determine the "effective length" of the breathing hairspring. The engraving below is meant to be a scale of sorts, to determine the regulator's position. The letters, as dedestexhes stated, indicate the directions for "fast" and "slow". This is why it is called a "swan-neck regulator".
However, there is a modern alternative to using a regulator which is the freesprung balance. This means there are no regulator pins that interfere with the hairspring breathing, thus it is "freesprung". Timekeeping is instead controlled via adjusting the position of masses on the balance wheel - the further out the weights, the higher the inertia and thus the slower the watch beats and vice versa. This, in theory, provides better timekeeping because of better isochronism and less susceptible to orientation/gravity effects.
Now, if the weights are used to adjust the beat rate for a freesprung balance wheel, then what is the purpose of the swan-neck? The answer is that it adjusts the starting position of the hairspring instead, to ensure that the "tick" and "tock" of the balance wheel swing in equal amounts and are not lopsided. This is called the "beat error". There are occasions where people mistakenly still call this a "swan-neck regulator", when it doesn't apply here and would simply be called a "swan-neck"!
Ideally, beat error only needs to be set correctly once and can be left alone - this is because the geometry of the spring won't easily change over time. Therefore, the balance cocks of freesprung watches do not have a scale engraved into it, instead they use the entire cock as a full canvas for ornate engraving.
Meanwhile, as we all know, a watch may gain or lose time over the years due to many factors. A watchmaker would have to regulate it every now and then for accurate timekeeping. Thus, for the non-freepsrung watches, the swan-neck regulator serves a functional purpose for timekeeping adjustment and thus the scale makes sense.
The differences can be seen in the photos below - the top is from a Lange Sax-0-mat movement, while the bottom of a RL Jumping Seconds. The Sax-0-mat is an older movement, thus retains the regulator and hence the engraved scale. Meanwhile, the RL series of watches are all about chronometric performance, thus it uses a freesprung balance wheel and hence no scale is needed. Most modern mid-high end Lange watches adopt the freesprung balance, including updated movements - the 2nd gen 1815 Chrono and the Datograph U/D for instance.
In short, if your balance cock has a scale engraved on it, it is a regulator watch. If it is fully engraved head to toe, it has a freepsrung balance wheel instead!
Regards,
skyeriding