Luminosity diagrams for the C¹⁸O and ¹³CO lines in our models. Upper left: model fluxes are grouped by disk mass and contours outline the regions where models of corresponding mass reside. Upper middle: models are colored according to characteristic radius. Upper right: Models are colored according to stellar mass. Lower left: distribution of uncertainty in disk mass. Lower middle: uncertainty in characteristic radius. Lower right: uncertainty in stellar mass. Uncertainty here is defined as the ratio of maximum and minimum parameter value within 10% range of luminosities of the point on the diagram. White means there are no models nearby.