Movement of a pendulum or oscillating body between two extreme positions (A' and A'').

The balance of a mechanical watch generally makes five vibrations per second, equivalent to 18,000 vibrations/hour (2.5 Hz). A more accurate mechanical watch makes 10 vibrations per second or 36,000 vibrations/hour (5Hz). A quartz watch makes 64,000 vibrations per second ( 32 MHz).

An oscillation (« tick-tock ») equals two vibrations (although oscillation is sometimes incorrectly used to refer to a vibration).