News & Events
Careers at IWC
Da Vinci Family
Portuguese Sidérale Scafusia
Retail & Service
Where to find us
Service and Support
Product Manuals and Guarantee
Sign Up for the IWC Newsletter
> If you are ...
If you are concerned about accuracy….
April 17, 2005
Michael referred to Walter Odets as mentor and guru. So when I saw Walter’s name popping up in a recent search I did on “Portuguese”, “IWC”, “History”, I could not resist reading the article. The article was part of a series about “Tweaking the Mark XII” (see link below; part about accuracy is in 2.1). There is one part that I wanted to share with those being concerned about the accuracy of their watches and did not see Walter's article yet. His writing helped me understand the concept of accuracy better.
Walter says “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”.
He then says that 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”.
I do hope Walter does not mind sharing his words with you.
to be continued..
April 17, 2005
If you are concerned about accuracy….(2)
Walter describes the following parameters:
Stability of rate in a single position (SRSP)….. 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. …
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? ……. as anyone who has used an electronic watch timer knows, watches are surprisingly variable--and sometimes absolutely quirky--even in this relatively easy specification. ……. In other words, in practice, averaging all error together never produces a perfect result, even if theoretically it might. …………. 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).
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." ……..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).
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.
April 17, 2005
On adjustments Walter says: "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.
I kindly refer you to Walter's article for further info.
April 17, 2005
130 Discussions and Comments
Member since Jan. 25, 2004
Thanks great article, makes things clear
April 18, 2005
71 Discussions and Comments
Member since April 22, 2004
Thanks for passing along these thoughts.
An interesting perspective that makes a lot of sense.
April 19, 2005
3,875 Discussions and Comments
Member since April 17, 2001
Thanks for your input!
Last edited: 6 July, 2012 - 10:18