Using energy intensity as a measure, the U.S. is using slightly more than 9, 000 BTUs per dollar of GDP.

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Of course, the use of energy intensity as a measure is not perfect and the results can be misleading.

FORBES: The Most Energy-Efficient Countries

It also can record the point where ball meets racket, rate your consistency and measure intensity (shots per minute and amount of actual playing time, rather than time on court).

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In a provocative new study, scientists reported Wednesday that they were able to "see" pain on brain scans and, for the first time, measure its intensity and tell whether a drug was relieving it.

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As part of its most recent five-year plan, Beijing set an ambitious goal to reduce its energy "intensity"--a common measure of a country's energy efficiency--by 20% from the 2005 level by 2010.

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The risk is that you then feel that love has died because, following the romantic myth, you measure love by its felt intensity.

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The island nation uses 4, 500 BTUs per U.S. dollar of gross domestic product, a measure known as "energy intensity, " the world standard for measuring how efficient an economy is at using energy.

FORBES: The Most Energy-Efficient Countries