For the post on why mechanical watches have timing errors, the main sources of error in mechanical watches are isochronous errors and positional errors. In fact, the error is closely related to the size of the balance wheel's amplitude. I've also seen some very meticulous people who have observed and tested their own watches, even recording the daily timing errors. Some people have very high demands for the precision of mechanical watches. In fact, a watch with an error of less than 10 seconds per day is already quite accurate, but there are still people who think it's not precise enough.
The timing accuracy of a mechanical watch cannot be achieved or maintained through correction. Why is this? It's because the timing of a mechanical watch is constantly changing. For a given state of the mainspring's tension, a fixed position, and a certain temperature, it may temporarily be accurate, but under different conditions, it will change immediately. This means that even if you adjust your watch to be perfectly accurate at one second, you'll find it won't stay that way. The precision is always changing instantaneously and fluctuating. Moreover, there are many other factors that affect the accuracy of a watch. The error we see in watches can only be an average error over actual operation and within a unit of time.
A watch has the best timing accuracy when the mainspring is fully wound. To ensure your watch runs accurately, you should wind the mainspring as much as possible, which is especially important for automatic watches. This is because the degree to which the mainspring of an automatic watch is wound is directly related to the amount of time and movement during wear. The condition is that there must be sufficient movement.
A watch has different timing accuracies in different positions. This is what we call positional errors in watches. Better watches are tested in three temperatures and five positions when they leave the factory. The five positions are: face up (dial facing up), face down, crown down (3 o'clock down), crown left (12 o'clock down), crown up (9 o'clock down). The only position not commonly used is crown right (6 o'clock down) unless you wear the watch inside your hand or on your right hand. According to statistics, most people use the face-up position about 35% of the time in a day, crown left 30%, crown down 25%, and other positions 10%. Therefore, by using the different precision errors of a watch in different positions, you can correct the tendency of the watch to run fast or slow.
First, conduct an observation test and record the results. The testing method is simple. You need to fully wind the watch first, then synchronize its hours, minutes, and seconds with a standard time. Then place it in a flat position for 24 hours of actual operation, and compare and record the error with the standard time. Repeat this process sequentially for the watch’s face-down, crown-down, crown-left, and crown-up positions, recording the operational error each time.
For example, the static test results are: face up +20 seconds/day, face down +20 seconds/day, crown down -5 seconds/day, crown left +25 seconds/day, crown up +10 seconds/day. The result is that the actual timing error of the watch while worn is +15 seconds/day.
Choose the position to place your watch at night to correct the error. Taking the situation in the above example, it is clear that placing the watch with the crown down at night will help reduce the cumulative timing error of the watch. Only by having a correct understanding of the causes of errors in watches and the characteristics of errors in your own watch can it serve you better.