A nomogram (Greek: νόμος – law and γράμμα – writing) is a graphical representation of a function of several variables, which allows using simple geometric operations (for example, applying a ruler) to study functional dependencies without calculations, for example, solve a quadratic equation without applying formulas.
Geometric images of dependencies between variables, eliminating the need for calculations, have been known for a long time. The development of the theory of nomographic constructions began in the 19th century. The first was the theory of constructing straight-line mesh nomograms by the French mathematician L. L. Lalanne (1843). The basis of the general theory of nomographic constructions was given by M. Okan (1884-1891) – in his own works the term “nomogram” first appeared, which was established for use in 1890 by the International Mathematical Congress in Paris.
The peculiarity of the nomograms is that each drawing depicts a given region of variation of the variables and each of the values of the variables in this region is depicted on the nomogram by a certain geometric element (point or line); images of the value of variables associated with a functional dependence are on the nomogram in a certain correspondence, common for nomograms of the same type.
Nomograms are distinguished by the way the values of the variables are displayed (dots or lines) and by the way the correspondence between the images of the variables is set.