This dialog is available from the Graphs / Options / Overlaid Portfolios... menu command.
This dialog box allows you to select the portfolios that will be overlaid for the Portfolio/Investment(s) Overlay graph types. Highlight the portfolios to overlay. The "Reference Portfolio" is used for calculating the hypothetical value for each overlaid investment in the Portfolio / Investment(s) Overlay - Value" graph type.
This dialog box selects which portfolios to overlay. To actually overlay the portfolios you must select one of the "Portfolio/Investment(s) Overlay" graph types from the Graphs menu.
Selecting Investment to Overlay