A nomogram, also called a nomograph, alignment chart or abaque, is a graphical calculating device. The field of nomography was invented in 1884 by the French engineer Philbert Maurice d’Ocagne (1862-1938). Nomographs have been used extensively since its invention to provide engineers with fast graphical calculations of complicated formulas to a practical precision.

## How Do Nomograms Work?

Nomograms use a parallel coordinate system rather than standard Cartesian coordinates. They consist of a set of n scales, one for each variable in an equation. By knowing the values of n-1 variables, the value of the unknown variable can be found.
The two-dimensional diagrams allow the approximate graphical computation of a function. The result is obtained by laying a straightedge across the known values on the scales and reading the unknown value from where it crosses the scale for that variable. The virtual or drawn line created by the straightedge is called an index line or isopleth.

## Using Nomographs for Pipe Sizing

Nomographs have many applications. One such application is for determining the size of a pipe. See the following video:

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