ABSTRACT
These differences can perhaps be better understood by comparing the operation of the abacus with that of the slide rule. In the abacus, quantities are represented by a number of beads, thus the quantity being represented can only vary, up or down, by a minimum of one bead-there are no partial beads. Furthermore, the abacus is an arithmetic machine, in which all operations are performed as a series of additions or subtractions. In contrast, slide rules represent quantities as continuously varying magnitudes: in this case length. Results are obtained by adding or subtracting measured lengths. The granularity of the result is limited only by the coarseness of the scale used to perform the measurement. Though in practice the slide rule worked by adding and subtracting lengths, they were fundamentally mathematical devices which operationalised logarithms: a mathematical function that was used to facilitate multiplication and division.
