ruler

a tool used for geometric constructions, linear measurements, and calculations. A scale (or scales) is usually marked on a ruler, the value of which depend on the purpose of the ruler. For convenience, some rulers have reference data (magnitudes of physical values, multiplication tables) or special attachments. For instance, rulers used in cartography have a magnifying glass that can slide along the ruler. Rulers used for geometric construction and measurements include straightedges, try squares, and shaped rulers (for instance, officer’s and navigator’s protractors, stencils), as well as French curves. In industry, rulers are used to measure linear dimensions in specific units (for instance, points in printing). Rulers are also used in technology for various purposes. For instance, a shrink ruler serves to compare specified dimensions and actual dimensions (in foundries, textile production). A straightedge is used to check the linearity of generating lines or the smoothness of surfaces in manufactured articles. A tape measure is used for measuring large lengths or diameters. A ruled scale is used to change from one scale to another. A slide rule is used for mathematical computations.