How accurate can I expect my mechanical watch to be?
This is truly a Frequently Asked Question, in that people will post that they have just purchased a new watch, and it gains/loses X seconds per day - they then ask whether this acceptable for this brand or model.
After reading several articles on this subject, we've come to the following conclusions:
Just about any current production watch is capable of running overall within 15 seconds deviation or less per day - this includes relatively inexpensive brands, as well as high-end brands like Patek, JLC, and Lange.
The stability of a given rate can be quite ephemeral, with the instantaneous rate even in a single position varying constantly. This means that the rates for a given watch are constantly drifting - although for higher grade movements the amount of drift tends to be much smaller.
The question of accuracy is more subtle than it appears on the surface. The reason is that, due to the limits of how small components can be, forces will act on the components differently when worn on the wrist vs. when resting in any particular position. In other words, even a watch which has a daily error rate of 4-5 seconds/day in any single position can be made to show zero overall drift though the combination of wearing the watch and letting it sit overnight in a particular position to compensate for drift obtained during wear.
A higher quality watch may or may not be more accurate than a lower quality watch at any given instant in time, but it has the potential to be more accurate. The reason is that a higher quality watch has been adjusted to minimize the variation in error in several positions, and has less drift in the rate over time.
It is a relatively simple operation for a watchmaker to adjust a watch that runs consistently fast or slow to near zero error. This operation, which is called regulation - merely increases or decreases the overall rate without compensating for rates in positions.
Also, the conventional wisdom is that a typical new watch needs to be run-in - in other words, while sitting unused in the jeweler's shop, lubricants pool in certain locations. It takes a couple of months for the lubricants to be properly redistributed, and for the motion to wear away some of the microscopic imperfections that all parts have.
Bottom line - let a new watch run for about 2 - 3 months before taking it in to be re-regulated.
(portions used with permission of TimeZone)