I've seen a number of posts in this forum from members who reported that their new watch ran fast. Typically they are reporting about +10 seconds per day. These posts are invariably answered by friendly suggestions that things will improve after break-in.
Have any of you actually observed a watch running slower after break-in than when you first received it?
That is the exact opposite of what I've observed when I buy a new or used watch. In both cases, it's likely that the watch hadn't been running for a while before it was shipped to me. I find that whenever they do change during break-in, it's always a change towards faster. I presume the lube is "un-sticking".
I enjoy regulating my watches, and because they usually speed up after break-in, I've stopped trying to regulate them until break-in is complete. It can take one or two weeks before they stop speeding up.
Another observation with ETA movements is that they run faster off my wrist. I attribute this to temperature effects. I believe that the hairspring shrinks slightly at lower temperature (off wrist) and thus has a faster natural period. So I regulate my watches on-wrist.
Listening to WWV on my shortwave radio and observing the second hand under a magnifying glass, I can estimate the time of the beep to an accuracy of about 0.1 seconds for a full diameter (sweep) second hand, and about 0.3 seconds for small seconds. Thus within a few hours of making an adjustment, I know enough to make another adjustment, if needed. With three to five adjustments I've adjusted four ETA 2824-2 watches to a daily error of less than 2 seconds. And their accuracy continues for months after that. I was amazed that a mechanical movement was capable of that, and wouldn't have believed it if I hadn't experienced it so many times.
I've discovered that one of my ETA 2824 watches does not speed up when off wrist, if stored vertical with the crown up, which is a very natural orientation when the strap is closed. I haven't check other watches with that movement yet.