Napier's Bones (Manual Calculator)

Napier's Bones is a manually-operated calculating device created by John Napier (1550-1617).

Using the multiplication tables embedded in the "bones", multiplication and divisions can be reduced to a series of simple additions and subtractions.

My words cannot do justice to this great little tool so I will let Wikipedia explain it for you, see examples on how to use :
http://en.wikipedia.org/wiki/Napier%27s_bones#Example_1

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