The short answer: it depends.
The accuracy of a vintage watch is at the at mercy of its original quality and construction, and accuracy owes even more to the quality of its upkeep over the years.
A high-quality, chronometer-grade watch that was carefully maintained and cared for over the years can approach chronometer standards still today. However, a more inexpensive design that had a greater degree of wear and tear in everyday life that wasn’t as well maintained might not be nearly as accurate..
Many of these old watches can be repaired and adjusted to run very accurately, there are simply some that are old, tired, worn out antiques. Some vintage watches are lucky to be running at all after the way they’ve been treated for three or more decades.
In general it’s perhaps unreasonable to expect a decades-old watch to perform like new, and a +/- 1 minute a day rate for most any 30-60 year old watch with unknown or even no previous service history isn’t too bad in my opinion, especially for watches that may not have been capable of chronometer performance when new.
A few things that will affect watch accuracy in a vintage watch
My ’57’ Chevy Rule
When I was a kid,there was an older lady that lived up the street from me. The only thing that I remember about her was the beautiful ’57’ Chevy that she had in her garage. She would only take the car out on a Sunday afternoon when the weather was perfect. I never saw that car in the rain.The car was meticiously cared for its entire life and is probably is great shape today. You might wonder what this car story has to do with repairing watches.
Well, every week I get a call from a prospective customer that has a vintage watch that is 30-40 years old and they ask me if I can get it back to good running order. My answer is usually “maybe”. I tell them it is hard to tell how well your watch may run until I have a chance to look it over. Sometimes they are a bit puzzled when they say that it is a fine quality Omega or maybe even a Rolex, they can’t understand why I can’t get it back to chronometer standards after my repair. I tell them if it is old and worn when it comes in, it is going to be old and worn when it leaves, it will just be cleaned.
Here is where the ’57’ Chevy comes into the conversation. Has this watch been cared for over the years, cleaned and oiled every few years, kept out of water, treated kindly and never abused?? If not, then it is hard for me to try and get it back to perfect running order. I always tell cystomers that I will do my best. Most of the time, the watch turns out fine, sometimes not so well. Please keep in mind that in order for any watch to run well, many parts need to mesh together perfectly. If the watch has a worn staff, bent or rusty hairspring, cracked jewel, loose or tilted roller jewel, and on and on, then the watch won’t keep perfect time.
Which Car do you think is going to run better after an oil change??