But running time can be extended by repeatedly winding up the spring and transferring its energy into the battery.

ECONOMIST: MONITOR

Repeatedly winding up the spring and dumping its energy into the battery (a process that takes about two minutes) can increase the total running time.

ECONOMIST: Clockwork technology

The so-called London Whale blunder weighed on shares heavily in the spring and summer, but with the year winding down the stock was just a few bucks shy of its 2012 highs.

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The small temple, which was a Christian Science reading room until the congregation bought it in the spring of 1992, is tucked back on a winding residential street in the northern part of the city, not far from the university that shares its name with the town.

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The final step is to do away with the spring altogether, and charge the battery direct from the winding action.

ECONOMIST: MONITOR