Circular Slide Rules

Circular Slide Rules

Circular slide rules, also known as circular calculators or circular slide charts, are mechanical devices used for performing mathematical calculations by sliding a circular disk around a fixed central axis. They were widely used in the pre-digital era, particularly in engineering, science, and mathematics fields. Circular slide rules consist of two or more concentric disks, each with a series of logarithmic scales and other markings. The outermost disk is usually fixed, while the inner disks can be rotated relative to the outer disk. To perform a calculation, the user lines up the relevant scales and markings on the disks, and reads the result from the appropriate scale. Circular slide rules were first developed in the late 19th century, and became popular in the early 20th century. They were particularly useful for performing complex calculations quickly and accurately, without the need for a pencil and paper. They were also portable and easy to use, making them popular with engineers, scientists, and other professionals who needed to perform calculations on the go. However, with the advent of digital calculators and computers in the 1970s, circular slide rules became largely obsolete. Today, they are mostly used by collectors and enthusiasts, although some professionals still use them for certain applications, such as calculating the correct exposure settings for photography.

mechanical devices, logarithmic scales, mathematics, engineering, obsolete

— Thomas Smith

CITATION : "Thomas Smith. 'Circular Slide Rules.' Design+Encyclopedia. https://design-encyclopedia.com/define/circular-slide-rules?E=299771 (Accessed on October 14, 2026)"