English: Normalized exponential integral. The value plotted is ${\displaystyle {\frac {\operatorname {Ei} (x)}{(\exp x)/x}}.}$ The values of ${\displaystyle x}$ are written above the corresponding point. The horizontal spacing is according to ${\displaystyle \arctan x.}$ The graph is extended "beyond infinity" a little on both the right and the left to show how the normalized function behaves when ${\displaystyle 1/x}$ is small. (The horizontal spacing for these points corresponds to angles whose tangent is ${\displaystyle x.}$)