I have a mechanical self-winding watch, which I got as a birthday present, two birthdays ago. In all the time I’ve had it it has kept terrible time. I checked it last year, setting it to the right time on 22 Feb then finding it 7:15 fast after 22 days and 4:52 fast after another 14 both of which suggest it’s gaining about 20 seconds per day. I’ve tried to have it corrected before but they take have to take the watch away for ages to do that, and when it comes back it’s no longer waterproof. So I’ve just got used to the fact that I need to reset it regularly; it’s invariably a bit fast; and if I need to know the exact time, I look at my phone.
Today I decided to fix it myself. You can do it the traditional way (make tiny adjustments then wait a day between each) but why would I do that when there is a fast, high-tech way?
The idea is you put the watch up to the microphone on a laptop, record the sound of it ticking for a minute then open up the recording in an audio editor (I used Audacity) and spot the tick marks (I used a high-pass filter at ~1kHz and 38dB amplification to make them easier to see), my watch ticks 6 times per second so then you trim the sample so that it starts exactly on a tick and measure the time until the 360th tick (in practise you don’t have to to count them, it will be the tick closest to the minute mark). Adjust the watch and repeat until the 360th tick happens exactly 1 minute in to the sample.
|Before adjustment||Time of 360th tick||Error||Seconds gained per day|
You could measure the speed of the watch to any accuracy you liked with this technique. Once the tick falls exactly on 60s (as closely as can be measured since the tick has a duration of about 8 miliseconds), then you could just extend the measurement period out. The problem is that the adjustment mechanism is just a lever with no scale. I took pictures of the mechanism between each adjustment, and it helped a bit. You can see the letter ‘s’ just underneath the adjustment lever which gives some sort of datum.
Here are the different adjustments. Subtle, hey?
You might notice that my table predicts the watch gaining almost a minute per day before any adjustments but my measurements of the actual watch showed it only gaining 20s. I can’t explain that so there is a chance I’ve made things much worse. That could possibly be because the watch isn’t designed to do an exact number of ticks in a second or minute, perfectly possible because all the hands sweep rather than step.