Hairspring measures the precision of mechanical watches.
Every mechanical watch has a hairspring and balance wheel, oscillating back and forth at a constant frequency. This keeps the time, and meanwhile makes a tick-tock sound. Hairspring measures the precision by analyzing the tick-tock sound, using the microphone of the smart device.
It supports wide range of frequencies:
Place the microphone tightly close to the watch back. Usually, as shown below, it is a good idea to put the microphone on some soft material, then put the watch onto the microphone.
When placing the microphone, make sure the side with a microphone mark is toward the watch back. Also make sure there is a good contact between the watch back and the microphone.
Tap the settings button to set the measuring time and the watch's frequency.
The measuring time is how long Hairspring takes to calculate the precision. The shorter the measuring time is, the faster the result will come out, but with a lower accuracy. The longer the measuring time is, the slower the result will come out, but with a higher accuracy. Usually, a measuring time of 30s is enough to get a ±1s/day accuracy.
The frequency of the watch is how many times the balance wheel oscillates forth and back in one hour. It is usually expressed in VPH (Vibrations Per Hour) or BPH (Beats Per Hour). Reference the watch's manual to get the correct value. If not sure, use Auto Detect.
If the signal is detected, the oscilloscope may look like this:
The small red bars denote where the tick-tocks are detected.
After collecting enough data, the result will be shown.
Hairspring is designed to be extremely sensitive to sound, especially to high-frequency sound. Finding a quiet place helps a lot to get a reliable result.
Though a longer measuring time helps to get a more accurate result, it is more likely to be affected by noises, which means if a noise goes into the system, it will affect the result for longer time if we choose a longer measuring time.
In a noisy environment, a shorter measuring time helps to get a more reliable result, though with less accuracy.
The oscilloscope shows the waveform of the signal, with a length of exactly 1 second. It will automatically amplify the signal to a proper amplitude for easy observation.
The frequency of the watch can be calculated from the oscilloscope. For example, in the above picture, there is 6 tick-tocks in 1 second. So the watch's frequency = 6 * 60 * 60 = 21600 (VPH).
The noise level can also be told from the oscilloscope. The above one has little noise. In contrast, the following one has more noise, but tick-tocks can still be detected.
If there is too much noise, find a quieter place, or adjust the placing of the microphone.
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