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:
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—Rutherford Birchard Hayes (1822–1893)
“Common experience is the gold reserve which confers an exchange value on the currency which words are; without this reserve of shared experiences, all our pronouncements are cheques drawn on insufficient funds.”
—René Daumal (1908–1944)