a device used for
rapid numberical calculations that involve mainly
multiplication and division
A slide rule typically consists of a ruler
with a sliding middle section. Both the ruler and
the slide have similar logarithmic scales printed
on their corresponding edges. An indicator made
of transparent material, with a vertical line
down the middle, is used to fix corresponding
points on the scales.
Slide rules were first devised in the
seventeenth century, following the invention of
logarithms by John
Napier. The integration of logarithms into
the existing repertoire of calculating devices
was sealed by the English mathematician Edmund
Gunter, who published his account of a
calculating instrument using logarithms in 1623.
Gunter described a set of single scales. To use
these a pair of dividers or compasses was
required, with which the quantities were stepped
out along the length of the scale. The straight
slide rule (such as the one shown above) was
invented by English mathematician William Oughtred.