Glossary
What a watch rotor is
watch rotor
A watch rotor is the semicircular weighted oscillating mass in an automatic movement that spins with wrist motion and winds the mainspring.
What you are seeing
Through an exhibition caseback, the rotor is usually the large decorated weight swinging across the movement. Some rotors are skeletonized or engraved; function is the same: convert motion into winding.
Ownership notes
Rotors can create faint winding sounds — normal on many movements. Ball-bearing vs older bushing designs feel different. Manual-wind watches have no rotor, which is one reason they can be thinner.
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