Mechanical watches on the extremely high end of the spectrum run at a frequency of ten Hz or more and measure time down to 1/20th of a second. That’s extraordinary, though—most mechanical watches run at 2.5 to 4 Hz (18,000 to 28,800 vibrations per hour), which is more than enough for accurate, dependable timekeeping. (It’s worth pointing out that quartz watches, in comparison, are orders of magnitude more precise than any mechanical watch—quartz crystal vibrates at 32,768 Hz.) More here.
A subject that is often not even considered, but there is some good information in the above article. Worth a read.