Jerome Lafontaine, age 93, of St. Albert, Ontario, Canada, for his question:

WHAT IS A SLIDE RULE?

A slide rule is a tool that is used for rapid numerical calculations that involve mainly multiplication and division. It looks very much like a ruler although there .are also some circular slide rules with movable discs attached.

The slide rule can solve problems of multiplying, dividing, squaring, cubing and extracting square and cube root. Some have additional scales for working out more complicated problems. Logarithmic scales are used for multiplying numbers.

To use the slide rule for either addition or subtraction, arrange two equally divided rulers with the zero of the lower scale below the number 4 on the top scale. The numbers on the top scale are than 4 larger than those on the lower. Slide the lower scale to divide.  With the introduction of electronic calculators, slide rules became things of the past.