'Otis King Calculator', cylindrical slide rule, England, 1920-1939

`Otis King Calculator', cylindrical slide rule 1920-1939, owned and used by the statistician Gwen Cartwright, the first woman to graduate in statistics, who worked for the Eugenics Society, the MRC, Rowntree, Leeds University and the Ministries of Food and Agriculture.

A slide rule is used for multiplication and division of numbers and is accurate to four decimal places. It uses a logarithmic scale which represents numbers as distances along a line. Typically slide rules are straight but the ‘Otis King Calculator’ was designed to have extra length through the use of a spiral along the outside of a cylinder. It was one of the most popular models until slide rules were replaced by electronic calculators in the 1970s.

This slide rule was owned by Gwendolen Cartwright (1898-1979), the first woman to be awarded a degree in statistics in England. Her work as a statistician was varied, for instance working for the Eugenics Society on a survey of deprived families in Bethnal Green in London.