<P> This is also applicable to circuits . Since signal progression in IC chips is very rapid, on the order of nanoseconds, a shake is good measure of how quickly a signal can progress through an IC (integrated circuit). </P> <P> Like many nuclear units, it is derived from top secret operations of the Manhattan Project during World War II . The word comes from the expression "two shakes of a lamb's tail" or, in the Southern United States, "three shakes of a billy - goat's tail," which indicates a very short time interval . For nuclear - bomb designers, 10 nanoseconds was a convenient specific interval to connect to this term . </P> <P> It has been discussed at length that the oldest documented usage of the phrase "two shakes of a lamb's tail" can be found within the compiled works of Richard Harris Barham called The Ingoldsby Legends (1840), but likely existed in modern language long before then . </P>

Where does the saying 2 shakes of a lamb's tail come from
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