'''Pi seconds is a nanocentury.''' 

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This excerpted from http://www.programmingpearls.com/sec071.html

You might find it hard to memorize that there are '''3.155x10e7 seconds in a year'''. On the other hand, it is hard to forget Tom Duff's handy rule of thumb that, to within half a percent, '''pi seconds is a nanocentury'''.

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See also: RuleOfThumb, RuleOfSeventyTwo, WhimsicalUnitsOfMeasurement