TWEAKING THE MARK XII: PART 2.1
THE CONCEPT OF TIMING
by Walt Odets
Having switched the original Mark XII caliber 884 for a caliber 887 (see “Tweaking the Mark XII: Part 1“), I spent in excess of 50 hours tweaking the escapement of the 887 to see if I could improve on the already excellent performance of this movement as delivered from the factory. In Part Two of the Mark XII/887 story I will discuss the timing and adjustment of watches in considerable detail. I have thus divided the discussion into three parts. This first part, 2.1, is about the concept and meaning of watch timing and adjustment; part 2.2 will elaborate on the the functioning of the escapement and the technical concepts used in adjusting a watch (see also, “The Escapement” in the Horologium); and part 2.3 will detail the long–and sometimes arduous–history of adjustments carried out on the Mark XII/887 and the results obtained.
ABOUT ACCURACY
There is no subject that, even among sophisticated watch collectors, is as misunderstood as timing adjustments to a watch. People routinely speak of “accuracy” as if it were a unified concept, and judge a watch heavily on the criterion. The term is usually used to mean simply that the watch compares favorably to a time standard in whatever unspecified way the owner happens to have compared it. When a watch does not compare well–adjusted at the factory with no idea of how the ultimate owner will use it, shipped from Switzerland half way around the world, and stored for months or years in a dealer’s showcase–the owner is disappointed and deems the watch “inaccurate.” The idea that one watch is “more accurate” than another because it gains two seconds a day, while the other gains eight, is a naive and simplistic approach to judging the quality–and the timing–of a watch. By this standard, unadjusted watches often appear to perform better than fully adjusted watches, which by any informed understanding they rarely do.
WHAT IS REALLY BEING MEASURED
“Accuracy” is used to imprecisely describe a group of four, essentially separate, parameters–parameters that, when taken together, determine the ability of a watch to match a time standard with relative consistency in specified kinds of use. An understanding of the real parameters behind the popular idea of accuracy will allow a finer appreciation of watches, help the collector judge the quality of a watch, and give him a sense of what is necessary to correct a problem with timing should it occur. These four parameters are my own construction and are not traditionally described in the literature on timing and adjustment. They are, however, useful concepts and underlie all timing and adjusting procedures.
The first of the four parameters behind the idea of accuracy is stability of rate in a single position (SRSP). One would like the rate of a watch in, for example, a (stationary) dial-up position to be be as stable as possible. But no mechanical watch meets this criterion absolutely, and the rate of very good watches fluctuates constantly. The SRSP of a very finely made watch may deviate over a range of four to eight seconds (calculated as deviation from absolutely correct rate, per day). The deviation of a less well made–or less well set-up–watch may span as much as 20 seconds or more. On an electronic timer, the rate of any mechanical watch–calculated and displayed as seconds plus or minus per day–fluctuates continuously. But it is important to emphasize that the SRSP parameter has, in itself, no relation to “correct” rate. SRSP is simply about stability. SRSP is a measure of the (relatively) instantaneous stability of rate, with no regard to a time standard. Assuming no damage and good servicing, SRSP is largely a product of the refinement and quality of the escapement and particularly the escape wheel, pallets, and pallet lever. Without reasonably good SRSP, adjustment to positions and regulation of absolute rate are moot. SRSP is an adjustment issue (as opposed to a regulation issue).
The second parameter underlying accuracy is the stability of averaged rate in a single position (SARSP). If we average the rate of the watch over one five minute period, how close is this average rate to the average rate of any another five minute period? The second period may be measured consecutively with the first, or days later. We hope that the average rates will be relatively close. But as anyone who has used an electronic watch timer knows, watches are surprisingly variable–and sometimes absolutely quirky–even in this relatively easy specification. The averaging of rate over longer periods–but not long enough that state of wind becomes a factor–reduces the effects of uneven running reflected in the instantaneous fluctuations described by SRSP. But the “averaging-out of errors” that occurs is never perfect and over finite amounts of time involves a considerable element of chance. In other words, in practice, averaging all error together never produces a perfect result, even if theoretically it might. And any measured performance is only a sample that suggests performance over longer periods. In addition to the quality and condition of the escapement, the SARSP can be easily affected by the quality and condition of the entire movement, all the way back to the mainspring. SARSP is an adjustment issue (as opposed to a regulation issue).
The third parameter underlying the accuracy of a watch is the relative averaged rate in different positions (RARDP). This parameter necessarily includes SARSP (because measurements are necessarily made over time), with the addition that rates are compared not only between time periods, but between different positions. For the wristwatch, these traditionally include the two horizontal and three (of the possible four) vertical positions. For example, the averaged rate (SARSP) of the watch dial-up (DU) over a five minute period is compared to the averaged rate crown down (PD, for “pendant down”) over five minutes. RARDP is, of course, the performance in question when we speak of a watch being “adjusted to positions.” Averaged rate between time periods (SARSP) is also necessarily being measured in this specification (because a watch cannot be measured in two different positions simultaneously). If the SARSP is poor, positional performance cannot really be determined. RARDP is dependent on the refinement and condition of the escapement, the repair and condition of the entire gear train of the watch, and the very fine adjustments applied by the timer (meaning watchmaker responsible for timing) to the balance wheel, balance spring, balance spring collet, balance pivots, and regulator pins (if any). RARDP is the best predictor of the potential for the watch being regulated to maintain a rate consistent with a time reference in typical daily wear. RARDP is an adjustment issue (as opposed to a regulation issue).
Finally, the fourth and simplest parameter underlying the idea of accuracy is simply absolute rate (AR). In this context, absolute refers to the time keeping of the watch relative to a known time standard. Without good stability over time and between positions, absolute rate is a moot point because it cannot be reliably accomplished. With good stability over time and between positions, absolute rate is a simple matter of adjusting the effective length of the balance spring with the regulator (or, in the case of adjustable mass balances, the center of mass of the balance). Although absolute rate is the parameter most noticed by the watch owner–and it is, no doubt, important–it is the simplest to accomplish and is the end-product of other, more complicated parameters. For the watchmaker, a “rate adjustment” is a simple matter. AR is a regulation issue, as opposed to the adjustment issue pertinent to the first three parameters.
ADJUSTMENT TO POSITIONS
Watches that are “adjusted to positions”–usually five, but sometimes three, four, or six–are considerably more expensive than unadjusted watches. This is at least partially justified because of the time put into adjustments. But there is a relationship between cost and the number of adjustments because, for good reason, adjustments are usually done only on better movements. A well-made, expensive movement may or may not be adjusted; but a poorly made or inexpensive movement cannot be adjusted. But, despite their considerable extra costs, it is often observed that in daily use adjusted watches often seem to run at no better an absolute rate than many unadjusted watches.
The adjustment of watches–and final regulation for performance in terms of absolute rate–has everything to do with how they will and will not be used. All wristwatches of reasonably high quality can be adjusted to provide relatively consistent performance in one position (good stability of averaged rate in a single position). Because of this consistency, they can subsequently be regulated to provide relatively good absolute rate (AR) in a single position. Such an “unadjusted” watch is thus, in fact, adjusted and subsequently regulated in one position, usually dial up. Today, machine-manufactured and timed balance-spring-staff assemblies make this quite easy, even in relatively inexpensive watches. Forty years ago this was not true and inexpensive watches did not run as consistently, even in a single position, as they do today.
A watch “adjusted to a single positions” will provide a good absolute rate so long as it is used in the position it is adjusted to, or to the extent that errors in other positions fortuitously average each other out. When such averaging happens, the absolute rate may be quite good, despite significant inconsistencies of running. Many people who report good absolute rate for their watches are not aware that this is being accomplished by the averaging of relatively poor rates at different times and in different positions. Were the watch checked at different times of the day, it might be found to vary significantly.
By timing a strap wristwatch in two positions–dial up and crown down (PD)–a manufacturer stands a very good chance of providing a watch that appears to be “accurate.” Such two-position timing is also relatively easy with current technology. Placed dial-up at night–which can amount to nearly 50 percent of the running time of the watch–and hanging crown down during the day whenever the wearer is walking with arms hanging, the watch is likely to put in a good averaged performance. If by chance, activities vary on a particular day, the inconsistent rate is simply chalked up to chance. A doctor once told me that his faithful (and unadjusted) Omega watch “ran slow” only when he attended continuing-medical education classes. He attributed this error to his impatience and boredom with the class, but wondered if the watch could be corrected anyway. During classes, he was not only bored, but sitting uncharacteristically with his arm on a table for eight hours, the watch held largely in a crown right position (as seen from the movement side of the watch). Were he a regular desk worker, he would have long ago found that his watch “ran slow” and had the rate adjusted to account for the crown right position. In this case, he might have been complaining about the rate of his watch only on the rare day he spent away from his desk with the watch crown down.
The adjustment of a watch to five or six positions is intended to maintain the absolute rate of the watch with greater immunity to the variability of actual use. In other words, a fully adjusted watch is intended to run more consistently regardless of how it used. It is more independent of position than a watch adjusted to one or two positions. This does not mean, as some expect, that regulation of absolute rate will be perfect from the factory for any particular owner. The full adjustment of a watch means simply that it is capable of such regulation because it can run relatively consistently in five or six positions. Because adjustments can never achieve identical rates in all five or six positions, individual habits will still affect the absolute rate of any mechanical watch.
CONCLUSIONS
In addition to the obvious pragmatic reasons for fully adjusting a watch, adjustment is an important–perhaps primary–component of watch craft. Even in the context of current technology, there is no watchmaker so exalted as the expert timer, and no watch so fine and refined as that fully adjusted to positions, temperature, and isochronism. The fully adjusted mechanical watch often seems infused with magic that defies the physics that would otherwise dictate its mortal limitations.
Throughout the last two centuries, the number of adjustments applied to a watch has been accepted as a primary measure of its quality. There is, no doubt, much reason behind this understanding, for the very fact that a watch can be adjusted in five positions is a measure of its quality. But there is a very important caveat here for the collector of contemporary watches. A watch can be “adjusted to positions” to any desired tolerances. Would it be correct to say that a watch adjusted to five positions and within 30 seconds per day from the slowest to the fastest position is fully adjusted? Probably not. In recent years, I believe some Swiss manufacturers have used assumptions about the traditional meaning of adjusted to positions to market watches that do not merit the designation.
In Part 2.2 of “Tweaking the Mark XII,” I will discuss the technical concepts underlying adjustments to a contemporary wristwatch like the Mark XII. In Part 2.3 I will discuss the actual history of adjustments to the Mark XII/887 in pursuit of possible improvement on the already excellent factory adjustments.
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