The Variables menu presents alternate variables for a selected plot type, and the menu contains different variables depending upon which plot is selected. For example, if a Mesh plot is selected from the Active plots list, then the variables in this menu will be mesh variables from the open file. If a pseudocolor plot is chosen instead, then this menu will contain variables suitable for pseudocolor plots, like density or pressure. If you have selected a pseudocolor plot and click on a variable in the Variables menu, then the pseudocolor plot will be redrawn using the new variable. This allows you to switch to a new variable while keeping the same attributes for the plot.