Similar to the pendulum in a pendulum clock, this regulating mechanism ensures a steady timekeeping rate in wristwatches. Comprised of a balance spring fixed to a weighted balance wheel, the device is connected to the mainspring. When the mainspring releases energy, it swings the balance wheel in one direction, called an oscillation, which tightens the balance spring. When the balance spring releases this stored energy, it propels the balance wheel back an equal distance in the opposite direction, transferring energy to the drivetrain, which powers the watch movement. The balance’s precise back-and-forth motion divides time into equal parts and is the source of the watch’s signature “tick-tock.”