When, by practice with logarithms, we become familiar with the correspondence between additions of length on the logarithmic scale (on a slide-rule) and multiplication of numbers in the natural scale (including fractional numbers), A /5 acquires a definite meaning as the number corresponding to the extremity of a length x, on the logarithmic scale, such that 5 corresponds to the extremity of 2X.
A slide rule should be used for the arithmetical operations, as it works to the accuracy obtainable in practice.
The rotating slide rule bezel is bi directional and and non ratchet.
The Chronomat is introduced in 1942 - the first chronograph to be fitted with a circular slide rule.
(SEE Logarithm.) The slide-rule (see Calculating Machines) is a simple apparatus for the mechanical application of the methods of logarithms.