Power Reserve Indicator
Some high grade watches have an extra dial on the face indicating how much power is left in the mainspring, often graduated in hours the watch has left to run. Since both the arbor and the barrel turn, this mechanism requires a differential gear that measures how far the arbor has been turned, compared to the barrel.
Read more about this topic: Mainspring
Famous quotes containing the words power and/or reserve:
“Many readers judge of the power of a book by the shock it gives their feelings—as some savage tribes determine the power of muskets by their recoil; that being considered best which fairly prostrates the purchaser.”
—Henry Wadsworth Longfellow (1807–1882)
“Her face had the seamed reserve of the old in this country [Japan]. It was a neighborhood poignantly rich in old ladies.”
—Angela Carter (1940–1992)