The Double-Y line plot can be considered to be a combination of two separately scaled multiple line plots. A separate line pattern is plotted for each of the selected variables, but the variables selected in the Left-Y list will be plotted against the left-Y axis, whereas the variables selected in the Right-Y list will be plotted against the right-Y axis. The names of all variables will be identified in the legend with the letter (R) for the variables associated with the right-Y axis and with the letter (L) for the variables associated with the left-Y axis. The Double-Y line plot can be used to compare sequences of values of several variables by overlaying their respective line representations in a single graph. However, due to the independent scaling used for the two axes, it can facilitate comparisons between otherwise "incomparable" variables (i.e., variables with values in different ranges).

See also, 2D Line plots, Graphs - 2D Line Plots and Exploratory Data Analysis and Data Mining Techniques.