With a “manual” watch, you’d have to wind it each day, whether you wore it or not,
to prevent it from running down and stopping; if it had a calendar, you might then
have to spend several minutes resetting it. But an “automatic”, or self-winding,
watch converted the natural motion of your wrist into energy to wind the watch's
mainspring; such watches often had no winding stem. So how would you keep it
wound if you weren't wearing it every day? You'd use a watch winder such as
this one, which simulated the movement of your wrist.