What is watch adjusting? When we buy a watch that says adjusted on the movement, what does that mean?
Adjusting is the craft of getting a watch to run accurately. When we adjust a watch, writes Hans Jendritzki in Watch Adjustment, we change it “so that the daily rate comes as near to zero as possible.” Cleaning, assembling, and oiling will get a watch ticking, but adjusting gets it running well.
Consider, for example, a vintage watch fan who winds up his Illinois pocket watch in the morning, puts it in the aptly-named watch pocket of his jeans, and heads to the office. Sometimes the watch is warm (when in the pocket); sometimes it’s cold (when walking outside or leaving it on a metal desk). If the watch’s crystal faces in, the watch will be vertical when he is standing but horizontal, with the dial down, when he’s sitting. It might also spend some of the day dial up, resting on a desk.
Likewise, consider a modern time-minded man who straps on a gentlemanly Hamilton Boulton in the morning, winds it fully, and faces the day. The watch will be in a bewildering number of positions, depending on the wearer’s arm movement.
And in both cases, the mainspring unwinds as time passes. The mainspring is fully wound in the morning and only partially wound at the end of day.
If we look at how watches get used, then, we see three factors that affect accuracy:
1. Position. Unlike clocks, watches move around. Any ticking watch can keep close time (a daily rate of zero) when left lying face up on a desk, but only an adjusted watch will keep close time in many positions. This aspect of adjusting is known as adjusting to positions or positional timing.
2. Temperature. The materials in a watch will expand and contract as they warm up and cool down, and serious changes in rate can happen when the balance wheel and hairspring change their shape. Although modern watches have largely solved this problem, compensating for temperature was something of an art in the vintage era.
3. Time since winding. Because the mainspring unwinds as the watch runs, the force it exerts varies across the day. A watch might thus be 3 seconds fast in the morning but 10 seconds fast in the evening. When a watch is adjusted for isochronism, its rate is consistent across time: the rate when the watch is wound will be the same as the rate 24 hours later. (A watch adjusted for isochronism won’t necessarily have a zero rate at both times—it might be 10 seconds fast at each time—but its rate will be consistent.)
The craft of watch adjusting is reducing the biasing effects of the Big Three sources of inaccuracy: position, temperature, and isochronism.
In the old days, getting watches to run accurately despite changes in movement, temperature, and time was crucial—it was how people made their meetings and how trains ran on time.
In modern times, adjusting vintage watches seems bizarre and quixotic. If we wanted an accurate watch, a cheap quartz watch or a stylish Accutron would keep much closer time than a 1920s pocket watch.
But watch adjusting is fascinating. It expands your knowledge of how watches work and gives you an appreciation for the talent and artistry of the old-timers, like the Illinois and Hamilton watchmakers who crafted strikingly precise watches 100 years ago, long before the invention of friction jeweling, timing machines, and Internet blogs.
So that’s what we’ll learn in this blog: how to adjust your watches so that they keep close time in use. We’ll focus on vintage watches, especially American watches from around 1900 to 1960. If your watch has pallet jewels and a balance wheel with removable screws, you’re in the right place.
After describing the basic ideas and tools, we’ll go through examples to see what adjusting looks like in practice. As our examples will show, with some patience and practice, you can adjust even old watches to surprisingly tight standards.