by Walt Odets


Regulator sweep measuresThe section of the balance spring “swept” by the regulator–the regulator sweep–is critical to the performance of the watch. As illustrated at right, the regulator itself must be moved away from the inner coils (dimension B) so that it does not foul the inner coils. This means that the outmost coil of the balance spring–which runs through the regulator–must also be moved away from the inner coils (dimensions C and D). Similarly, the stud holder (which provides the outer attachment of the spring) must not foul the coils. Thus, the stud is also moved away from the balance pivot (dimension A).

It is critical to the performance of the watch that the regulator sweep (yellow arrow) remain parallel to the other coils of the spring. In other words, dimensions C and D and all other points within reach of the regulator must be equal. If the regulator sweep is misaligned with the inner coils of the spring, the regulator will place pressure on the spring and decenter the inner coils (as discussed below). The left hand photograph below illustrates a poorly aligned regulator sweep. The right hand photograph shows the sweep after proper alignment.

Spring dog letAs illustrated at right (red section), for a flat balance spring, the position of the regulator sweep is determined by introducing a dog leg bend into the outmost coil of the spring before the regulator (i.e. between collet and regulator). The angles and proportions of the dog leg are critical both for the regulator sweep, and for the centering of the entire spring. Sometimes, an additional dog leg is used after the regulator (i.e. between the regulator and the stud), depending on the design of the balance cock and stud carrier. (The stud carrier and regulator are not always the same distance from the balance pivot.) With an overcoil spring, the overcoil section provides the function of the dog leg, and the latter is not used.


Regulators vary in design, but the most common today is the “single pin and boot,” as illustrated (in an inverted position), below left. The pin or index is indicated at the yellow arrow, the boot at the blue. The balance spring passes between these, dampening the Regulator, originaloscillation of the spring from this point to the stud. The regulator is thus determining the effective (i.e. oscillating) length of the spring. The length of the spring from collet to regulator determines the oscillating frequency of the spring. The point at which the regulator contacts the spring is also called the count point. The portion of the spring that lies “outside” the regulator (i.e. between the regulator and the stud), has only a minimal effect on the frequency of oscillation.

Regulator, adjustedFor the regulator to function as intended, the regulator index and boot must be parallel to each other so that both contact the spring along it’s entire height; the index and boot must be close enough together that there is as little play as possible short of binding the spring; and the spring must be positioned so that it is centered between the index and boot. The illustration aboveleft shows a regulator as supplied by IWC. The illustration at right shows the same regulator adjusted for better parallelism and spring contact. Final spacing and alignment was made after installation of the regulator and balance spring, and this regulator required some opening up in the watch.

The more restricted the spring is between regulator and index, the more effective the regulator is in “shortening” the spring to the count point. Decreasing the space in which the spring operates increases the rate of the watch by making the spring effectively shorter. When the index and boot are out of parallel, one consequence is a difference in rate between dial up and dial down positions. Vertical positions also become unpredictable. The photographs at left show a regulator with out-of-parallel index and boot. As the spring rises and falls in theregulator (with changes in the position of the watch), the amount of space in which the spring is operating changes, causing unintended changes in rate. With the adjustment in these illustrations, the watch would show a faster rate dial up (top photograph).

Assuming that index and boot are kept parallel, slightly increasing the space in which the spring operates is sometimes used to slow the rate in vertical positions (relative to horizontal ones). The increased space increases the effective length of the spring, and the effect is greater on vertical positions because of the lower amplitude in vertical positions, and because the increased space reduces the pressure of the vertical spring against index or boot. (In vertical positions, the weight of the spring presses the spring against index or boot, increasing the effectiveness of the regulator.)

One final aspect of the regulator should be described. The function of the boot is to close the space between index and boot at the otherwise open end so that a shock to the watch does not displace the spring from between the index and boot. The back of the boot is slanted so that if a shock forces an inner coil of the spring over the boot, it will slide off.


Centeringis a term used to describe two aspects of balance spring adjustment. The first, vertical centering, is about the “centering” of the spring vertically, or the flatness of the spring: how closely all coils lie in the same plane. The second, horizontal centering, is about the evenness and concentricity of the coils around the collet.


Balance spring, interferenceThe entire balance spring should be flat, all coils lying in the same plane. Poor vertical centering is usually evident as a “dishing” or doming of the spring; a damaged spring may show only one or two coils lying outside of the plane of the rest. In the illustration at right, it is just perceptible that the outer coils are progressively higher and the spring is slightly dished in the center. Such misalignment may cause the spring to contact surrounding mechanism in certain positions, and the red arrows show possible points of interference. While poor flatness is not good craft, it actually has very little effect on the adjustment of the watch–if it does not produce interference. In the above example, it is possible that in a dial up position some interference would occur. This would dramatically disrupt the adjustment of the watch.


Unlike vertical centering, horizontal centering is always critical to the adjustment of the watch. It is essential, for good positional performance, that the spring be perfectly centered on the collet, and that the coils be perfectly spaced and concentric with each other. Any irregularity in horizontal centering causes the spring to expand and contract unevenly and produce varied and unpredictable results in the various positions.

While a spring is normally perfectly centered as delivered from the manufacturer, it’s installation in the watch–including attachment at the collet and stud, and it’s routing through the regulator–will usually introduce distortions that must be corrected. In the Spring, centeredphotograph aboveleft, the regulator is placing outward tension on the entire spring (green arrow). The result is significant decentering, visible in the uneven spacing of the coils (red arrows).

As shown at right, re-centering of the spring required several corrections, accomplished by slight reshaping of the spring (with very fine #5 tweezers and a needle). These changes included reshaping at the stud (yellow arrow); moving the regulator sweep outwards (green arrows); and reshaping the dog leg (red arrows). At rest, the coils should be even and concentric, as shown. When the spring contracts or expands, the coils will be closer together or further apart, respectively, but the spacing between coils should remain even. Perfect centering allows the spring to “develop” smoothly and Spring, developingevenly, and minimizes the effects of shifts in the center of gravity of the spring as it expands and contracts.


The foregoing has been a basic introduction to the major principles of watch adjustment. In “Tweaking the Mark XII: Part 2.3,” I will discuss the application of these principles in the actual adjustments made to the Mark XII/887 in pursuit of improvement on the already excellent factory adjustments.


© 2012 Bourne In Time Inc.